*This is how I interpret the spell. I seek your feedback.*

SIMULACRUM
School: illusion (shadow); Level: sorcerer/wizard 7
Casting Time: 12 hours
Components: V, S, M (ice sculpture of the target plus powdered rubies worth 500 gp per HD of the simulacrum)
Range: 0 ft.
Effect: One duplicate creature
Duration: Instantaneous
Saving Throw: none; Spell Resistance: no

Simulacrum creates an illusory duplicate of any creature with which you are familiar. Familiarity is defined as killing/downing/defeating this creature in combat, or making a Knowledge check high enough to identify the creature, usually 10 + the creature's hit dice.

This creature, once formed, has half the hit dice of the original (minimum 1 hit die). This affects BAB, saves, skills, feats, spells known, ability score bonuses from hit dice, class features, base languages known, and other HD-dependent abilities. The caster determines the simulacrum's feats, skills, class features, spells known, ability score bonuses from hit dice, and other selectable abilities. Unless an ability states otherwise (like a Ranger's fighting style), the simulacrum must meet all prerequisites for all its abilities.

The simulacrum retains all abilities (supernatural, spell-like, or extraordinary) not derived from its original amount of hit dice, at their original caster levels. The DC may change because of the duplicate has fewer hit dice or a lower ability score. For example, a planetar is normally able to cast divine spells as a level 17 Cleric (level 16 in Pathfinder). A simulacrum planetar would still be able to do this, despite having only half its hit dice. If the caster who made the simulacrum planetar had a caster level too low to produce a simulacrum of its original hit dice (14 in 3.5, 17 in Pathfinder), the caster would need to remove 3 ability points (4 in Pathfinder) from the duplicate.

A simulacrum has the same size, types, and subtypes as the original creature. It understands and speaks the racial languages of the base creature. If the simulacrum has Speak Language ranks (Linguistics in Pathfinder) that it would lose because of lost HD, the caster determines which languages the duplicate knows from Speak Language.

You can't create a simulacrum of a creature whose HD or levels exceed twice your caster level.

You must make a Disguise check when you cast the spell to determine how good the likeness is with a bonus equal to your caster level. A creature familiar with the original might detect the ruse with a successful Spot check (Perception in Pathfinder) opposed by the caster's Disguise check or a DC 15 + your caster level Sense Motive check.

The simulacrum spell alone doesn't grant you any special means to communicate with it; for example, there is normally no telepathic link between the simulacrum and you. The simulacrum and you must have a common language or means to communicate.

While your simulacrum is loyal and will follow your orders to the best of its ability (even suicidal orders), it can be deceived or mind controlled just as others of its kind. You can command it to follow another's orders or act autonomously and it shall to the best of its ability. For example, a simulacrum of a human could be Bluffed or affected by dominate person just as the original human could. If ordered to act autonomously, it would act brilliantly or stupidly, depending on its INT, WIS, and Knowledge. If ordered to kill itself, it would by the most efficient means it understands and is able to execute.

A simulacrum can never increase in hit dice but can otherwise increase or decrease in power as normal for a creature of its types and subtypes: It can be healed as normal but dies at 0HP. (See below.) It can be enhanced or hampered by spells, permanent effects, and temporary effects. It can add spells to its spellbook. It can use magic items, and so on.

Regardless of its types or subtypes, if reduced to 0 hit points or otherwise killed/destroyed, a simulacrum reverts to snow and melts instantly into nothingness. Raise dead and resurrection won't revive a simulacrum but a miracle, wish, or true resurrection can.

Remember, the GM has the final say on what type of simulacrum you can make. GMs, remember simulacrum is meant to be a high level spell.

Seems to me like a rather reasonable interpretation of the spell.

I hate that it's so vague. I wish it would just say something like use creature's stats, but add a number of negative levels equal to half its HD, round up.

The simulacrum retains all abilities (supernatural, spell-like, or extraordinary) not derived from its original amount of hit dice, at their original caster levels. The DC may change because of the duplicate has fewer hit dice or a lower ability score. For example, a planetar is normally able to cast divine spells as a level 17 Cleric (level 16 in Pathfinder). A simulacrum planetar would still be able to do this, despite having only half its hit dice. If the caster who made the simulacrum planetar had a caster level too low to produce a simulacrum of its original hit dice (14 in 3.5, 17 in Pathfinder), the caster would need to remove 3 ability points (4 in Pathfinder) from the duplicate.

Not so sure I would allow this, in fact pretty sure I would not. At 13th level when you first get access to this ability, you could do a simulacrum of a Solar (23) hd. And have access to level 20 cleric casting and all sorts of "supernatural abilities".

I don't see anywhere in the actual description that it explicitly states the simulacrum gets supernatural abilities. As for the spell casting ability again I would not allow it unless it was from a creature with class levels which would be halved.

Despite the fact that it makes using Simulacrum more annoying, I wouldn't allow a planetar to have it's full casting in excess of it's HD. Spell-like abilities are a bit different, seeing as how a 1st level tiefling can cast Darkness, for an example.

It's scary how it's not capped, and I could see a character reaching twice their HD in caster level momentarily, thus being able to create fully powered simulacrum per CR.

But... mostly, I agree with your reading.

I disagree on only a couple of points:

The simulacrum retains all abilities (supernatural, spell-like, or extraordinary) not derived from its original amount of hit dice, at their original caster levels. The DC may change because of the duplicate has fewer hit dice or a lower ability score. For example, a planetar is normally able to cast divine spells as a level 17 Cleric (level 16 in Pathfinder). A simulacrum planetar would still be able to do this, despite having only half its hit dice. If the caster who made the simulacrum planetar had a caster level too low to produce a simulacrum of its original hit dice (14 in 3.5, 17 in Pathfinder), the caster would need to remove 3 ability points (4 in Pathfinder) from the duplicate.

I believe the caster level would be halved, even though it does not say so. This is, I believe, more in line with the intention of the spell. So a Planetar would only have a cleric casting ability of 8th. Same for the CL of the Spell-like abilities. However, SLA's and SU's still apply as normal. The level effects are just halved.

A simulacrum can never increase in hit dice but can otherwise increase or decrease in power as normal for a creature of its types and subtypes: It can be healed as normal but dies at 0HP. (See below.) It can be enhanced or hampered by spells, permanent effects, and temporary effects. It can add spells to its spellbook. It can use magic items, and so on.

I believe the intention of the spell is that the creation cannot be healed WHATSOEVER without spending the gp and using the magic lab. I think there is an edge case to be made for treating it as a construct and allowing the non-core Repair Damage spells to work, but Cure and Heal do not. Which makes more sense, considering it IS an arcane spell.

Other than that, I think you are spot on.

I believe the intention of the spell is that the creation cannot be healed WHATSOEVER without spending the gp and using the magic lab. I think there is an edge case to be made for treating it as a construct and allowing the non-core Repair Damage spells to work, but Cure and Heal do not. Which makes more sense, considering it IS an arcane spell.

This is why my wizard uses advanced troll fighter bodyguard simulucrums. They have regeneration and heal up just fine on their own.

The reason I object to the spell casting is it is not in the spell.

Here is the quote from the pathfinder Core book.

Simulacrum creates an illusory duplicate of any creature. The

duplicate creature is partially real and formed from ice or snow. It
appears to be the same as the original, but it has only half of the
real creature’s levels or HD (and the appropriate hit points, feats,
skill ranks, and special abilities for a creature of that level or HD).
You can’t create a simulacrum of a creature whose HD or levels
exceed twice your caster level. You must make a Disguise check
when you cast the spell to determine how good the likeness is.
A creature familiar with the original might detect the ruse with
a successful Perception check (opposed by the caster’s Disguise
check) or a DC 20 Sense Motive check.
At all times, the simulacrum remains under your absolute
command. No special telepathic link exists, so command must be
exercised in some other manner. A simulacrum has no ability to
become more powerful. It cannot increase its level or abilities. If
reduced to 0 hit points or otherwise destroyed, it reverts to snow
and melts instantly into nothingness. A complex process requiring
at least 24 hours, 100 gp per hit point, and a fully equipped magical
laboratory can repair damage to a simulacrum.

The part of spell casting spells and spell like abilities you see quoted above is how teh peson FEELS it should be written. With the orignal text I do not think that the planetar (or solar for that matter) would maintain such spell casting.

Now a GENEROUS GM could do a Savage Species type Progression for Solar, Planetar and Black Ethergaunt spelling out what they got at what HD. But from the text of the actuall spell, (Not how the OP interprets it and wrote his interpretation), I do not see it being within the scope of simulacrum.

Otherwise as the OP wrote it a level 13 wizard walks aroudn wih a simulacrum of a Solar (20th level divine caster) and a Black Ethergaunt (17th level arcane caster) and lets them do everything.

I think you have to fundamentally decide if the spell creates another party member or a 'Mook'.

Party member's might have advanced and interesting powers and spells.
Mooks would just be muscle and perhaps distractions, that turn to water like frosty the snowman at 0hp.

I think it depends on how rare\powerful the spell is and how much effort it represents in your game world.

A famous simulacrum Planetar get destroyed pretty quickly just because it made the real thing look bad.

A simulacrum has no ability to

become more powerful. It cannot increase its level or abilities.

I find this annoying but otherwise unambiguous. I don't think I would be able to add spells to my spellbook and such. I think in the adventure The Mask of Diamond Tears, an illusionist made several simulacrums(simulacrae?) of himself that could use spellbooks written with his lower level spells, but nothing was said of the duplicates researching new spells.

I do think for simplicity's sake that healing should work fine with me, as well as Dominate-type spells and protections or buffs and things. This is just my opinion, though. I noticed the spell description doesn't say just what type of creature I am supposed to be, so one could assume I should be treated like a construct or the type of creature I'm made to resemble.

Since a method of healing is mentioned in the text, it could be meant that normal healing and magical healing doesn't apply to me. I'm ok with that, I guess.