Two castings of Mnemonic Enhancer

Okay, here's the situation. I've cast Mnemonic Enhancer (prepare) twice. That means I've traded two 4th level spell slots for a 6th level one. (Even if you disagree with this, my GM doesn't so just work under the assumption that this is true.)
Can a 7th level wizard access a 6th level spell slot at all (with metamagic for example), or is this only useful to an 11th level wizard?
Does a 7th level cleric know 6th level cleric spells yet?
Could a sorcerer prepare spells this way or are they thwarted by not having a "normal" way to do so?

Finally, there's some flavour issues with this wizard spell being necessary to make a robe usable only by spontaneous casters.

Nothing can give you a spell slot higher than you normally can access except more levels in the class.

Hmm, it's a creative rule interpretation for sure.

Wizard, sorcerer and cleric sections in the Core Rulebook are like this:

A wizard can cast only a certain number of spells of each spell level per day. His base daily spell allotment is given on Table 3–16.

Table 3-16 says: Up to level 4 spells.

Since Mnemonic Enhancer already circumvents this when used for splitting up three spell levels in up to 3 additional prepared level 1 spells, it should be capable of adding higher level spells (assuming your combination of two casts is legal). As long as your Intelligence / Charisma / Wisdom are high enough.

But I doubt the spell is supposed to stack with itself:

Except in special cases, a spell does not affect the way another spell operates. Whenever a spell has a specific effect on other spells, the spell description explains that effect.

Same Effect More than Once in Different Strengths: In cases when two or more identical spells are operating in the same area or on the same target, but at different strengths, only the one with the highest strength applies.

Of course your GM could allow it, but it has drawbacks (reduces player's sense of achievement, provokes choice overkill, hurts game balance etc.). So personally, I'd be happy I had this smart idea but stick with the usual rules.

But I doubt the spell is supposed to stack with itself:

Core Rulebook wrote:

Except in special cases, a spell does not affect the way another spell operates. Whenever a spell has a specific effect on other spells, the spell description explains that effect.

Core Rulebook wrote:

Same Effect More than Once in Different Strengths: In cases when two or more identical spells are operating in the same area or on the same target, but at different strengths, only the one with the highest strength applies.

Of course your GM could allow it, but it has drawbacks (reduces player's sense of achievement, provokes choice overkill, hurts game balance etc.). So personally, I'd be happy I had this smart idea but stick with the usual rules.

Okay, thank you for your help. Since it's already been okayed, and I'm the player, I'll try not to break it so the rest of the table (and the GM) don't come to hate this decision. Maybe I'll just use it to quicken a third-level spell past 11th level. That's a pretty fair trade for two fourth-level spells right? Though, now that you mention it, I as a GM would obviously rule that two Rings of Wizardry don't stack. Hmm. Food for thought, and after this campaign a house-ruling will be made for all future ones.

Mnemonic Enhancer simply doesn't function that way although I understand your GM is allowing them to stack.

Regardless, you can't cast spells of a tier you don't have access to yet even from a bonus slot granted from another source. At best a 7th level Wizard can cast level 4 spells. This is clarified by the ability score FAQ stating spell slots for high ability scores aren't accessible until you cast cast at that level. However your GM homebrew'd approved this as well so...

Go ahead and cast Enhancer again a 3rd time (may have to wait a level or get a stat booster). This way you can access a level 9 spell slot like Wish spell coming online for you at level 8. Very broken indeed. Every NPC spell caster should use this combo, since its so much better than the alternative of memorizing naturally. The average life expectancy of a CR appropriate encounter is 3 rounds, so higher level spells coming back at you for 3 rounds is worse off for you in the long run than baddies that never really get to burn off their spells.

Trust me that at level 7 your wizard is really starting to come online and you don't need any kind of shenanigans to make them work.

Seriously, in a homebrew, I'd penalize the heck out of this even if I chose to allow it otherwise any village wizard can cast the most powerful spells with a small investment. I'm a fan of magic breaking the game, but only on a limited basis, and at a hefty price.

Ex. I allow the Wizard to do this once, but his mind is so badly scarred by it, he is effectively feebleminded (incurable INT damage except with rest time) at a result. This would allow a one time exertion to cast a powerful spell like Wish, to resurrect a comrade without it becoming an everyday occurance.

Simply put, it breaks power balance, wealth and everything else which really isn't your desire here. I doubt anyones abilities to create a cohesive world that makes sense allowing Enhancers to stack and cast above tier spell slots as powerful magics become available sooner for everyone allowing more powerful crafting, rich people that never die (to easy to bribe a local mage to cast Wish), ect..

Finally, Mnemonic Enhancer is a Wizard only spell and can't be used by Clerics or Sorcerers.

Since your GM is changing the rules of how the spell functions, ultimately they are going to have to be the ones who work out the holes this makes in the system.

Mnemonic Enhancer simply doesn't function that way although I understand your GM is allowing them to stack.

How does it simply work then?

At best a 7th level Wizard can cast level 4 spells....However your GM homebrew'd approved this as well so...

No he didn't. Where did I say that? Because I said that I was waiting until 11th level, when a Wizard normally gets his 6th level spell slots.

I think you misread things, or are confused. If the fault is mine for writing a confusing post, then I apologize.

And finally,

Finally, Mnemonic Enhancer is a Wizard only spell and can't be used by Clerics or Sorcerers.

Sure it can. You just need to add it to their class list first (and for Sorcerers, spells known). But those were examples anyway.

Since your GM is changing the rules of how the spell functions, ultimately they are going to have to be the ones who work out the holes this makes in the system.

He made a ruling, based on the information easily available at the time, and it's now accepted that I can do this. I made this post for clarity. If necessary, the ruling will be reversed, but if I don't be a jerk about it then it won't need to be. That's why I asked everyone to just accept that this were the case.

It allows you to exchange a 4th level spell for 3 levels of floating spells slots that must be prepared normally.

Examples:
-(3) 1st level slots
-Another 2nd and another 1st level slot.
-Another 3rd level slot

If you know you are going to need a lot of magic missiles today you can exchange a 4th level spell for (3) first level ones.

or,

You can cast to instantly recall any spell 3rd or less you just cast. This version allows the Wizard flexibility in spell preparation similar to a Sorc (but its not ideal since thats not what Wizards are built for)

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Your mind only has access to spell slots he is able to cast, so no 6th level slots until 11 for a Wizard, or 12 for a Sorc. If your GM didn't houserule this exception, I apologize as I misread your OP.

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No worries as the game is meant for variety. However, in this case I doubt it will stand as your fellow players won't like it when this particular strategy is pointed back at you if allowed.

As far as non-wizard use of the spell, you would have to add it to your spell list, or UMD a scroll.

I'll explore this a little as I think its interesting.

A cleric "casts" this. His mind is opened up to prepare more spells. Although a Cleric prepares spells, they are divinely granted. If the deity or minion decided to fill these expanded spell slots is up to GM fiat, but not expressly prohibited by the text. If cast from a scroll I believe it would grant wizard slots. If allowed onto the cleric spell list, it should open cleric slots, but thats just my 2 cents worth.

A sorceror "casts" it. Since they can't prepare spells the first casting option is wasted. The second option returns a previously cast spell to memory. A sorcerer never "forgets" a spell so I believe it would be wasted as well. I also believe this was intended as there is 99% overlap between sorc/wizard spells, yet sorcs don't have this on thier spell list. Its not unreasonable to allow a used spell slot to be returned but it would be homebrewed and impractical for most sorcs anyway.

Why use a level 4 slot to cast a level 3 spell, when the sorc can just use metamagic to spontaneously cast the level 3 spell (Extended) using a level 4 spell slot? It might add some flexibility in corner cases though.

1) Can a 7th level wizard access a 6th level spell slot at all (with metamagic for example), or is this only useful to an 11th level wizard?

2) Does a 7th level cleric know 6th level cleric spells yet?
3) Could a sorcerer prepare spells this way or are they thwarted by not having a "normal" way to do so?

You last post asked how it works.

1) Used by a Wizard you gain "three additional levels of spells". So a 7th level Wizard knows 4th level spells. He can learn 3 more magic missile today or one more fireball. But no 4th level spells and of course no 5th or 6th level spells.

2) A 7th level cleric doesn't know any 5th or 6th level spells at all.

3) Sorcerer can only use the retain ability, but since Sorcerers don't get the spell you would need to get it on their class spell list somehow.

@Grey_Mage I'm playing a Pathfinder Savant in a different playgroup (it's a cleric, too), but that's a pretty good way to add spells to class lists. The sorcerer might get use out of having three more magic missiles, instead of a single fourth-level slot, but that depends entirely on the sorcerer. Also, we're pretty sure that they have no "normal" way of preparing spells, so it's strictly impossible.

1) Used by a Wizard you gain "three additional levels of spells". So a 7th level Wizard knows 4th level spells. He can learn 3 more magic missile today or one more fireball. But no 4th level spells and of course no 5th or 6th level spells.

But I cast it twice, and it contains the word "additional" so I thought it made sense to use addition. The text doesn't give a maximum on the highest level of a single spell you can memorize. It's the fact that it uses a totally unprecedented floating level count. I totally understand saying no to this for reasons of RAI, but that's not my situation at the moment.

2) A 7th level cleric doesn't know any 5th or 6th level spells at all.

I suspected, but wasn't sure, that this was the case.

3) Sorcerer can only use the retain ability, but since Sorcerers don't get the spell you would need to get it on their class spell list somehow.

Okay, well that's better than trying to use your prepared slots to qualify things, and depending on casting this spell every 24 hours or wondering if the spell slot is still there when it's expended.

1) But I cast it twice ... The text doesn't give a maximum on the highest level of a single spell you can memorize.

Ok, 6 levels. But that doesn't mean you can gain a 4th level or higher slot. You would have 6 slots to memorize. You can never have slots higher than you can normally cast. Also, nothing stacks with itself anyway (except damage.) So even if you could cast 6th level spells (because 11th level Wizard) you couldn't do a 6th level spell because that would be stacking with itself.