Spells are not weapons. Vital strike doesn't apply to them.
Vital strike is applied only to weapon damage. It does not multiple any damage not caused by weapon damage dice. So, damage from strength bonus, favored enemy, and anything else that isn't the listed amount of damage for the weapon (with any appropriate changes for size) isn't multiplied.
As spells are not weapons Vital Strike cannot be used with them.
Also, Vital Strike requires its own special standard action to be used, and casting a spell normally requires its own standard action. They could not be used together even if the spell did count as a weapons.
Vital Strike is a standard action.
No, Vital Strike is a non-action that requires that you use the Attack Action. You could be holding the charge, then spend a standard action to take the Attack action...
...which still wouldn't let you use Vital Strike with a held spell, because despite the similarities, a held spell is not a weapon.
While looking at this, I noticed something interesting that I'd not seen before.
Holding the Charge: If you don't discharge the spell in the round when you cast the spell, you can hold the charge indefinitely. You can continue to make touch attacks round after round. If you touch anything or anyone while holding a charge, even unintentionally, the spell discharges. If you cast another spell, the touch spell dissipates. You can touch one friend as a standard action or up to six friends as a full-round action. Alternatively, you may make a normal unarmed attack (or an attack with a natural weapon) while holding a charge. In this case, you aren't considered armed and you provoke attacks of opportunity as normal for the attack. If your unarmed attack or natural weapon attack normally doesn't provoke attacks of opportunity, neither does this attack. If the attack hits, you deal normal damage for your unarmed attack or natural weapon and the spell discharges. If the attack misses, you are still holding the charge.
Emphasis mine.
Basically, you have two options: touch allies as a standard action (no roll necessary) or strike as normal with an unarmed attack (not a melee touch attack). I had always played it such that you simply held your melee touch attack until later and got to target touch AC on a held charge. It seems to quite not be the case. Interesting.
You may want to read this post
While looking at this, I noticed something interesting that I'd not seen before.
Holding the Charge: If you don't discharge the spell in the round when you cast the spell, you can hold the charge indefinitely. You can continue to make touch attacks round after round. If you touch anything or anyone while holding a charge, even unintentionally, the spell discharges. If you cast another spell, the touch spell dissipates. You can touch one friend as a standard action or up to six friends as a full-round action. Alternatively, you may make a normal unarmed attack (or an attack with a natural weapon) while holding a charge. In this case, you aren't considered armed and you provoke attacks of opportunity as normal for the attack. If your unarmed attack or natural weapon attack normally doesn't provoke attacks of opportunity, neither does this attack. If the attack hits, you deal normal damage for your unarmed attack or natural weapon and the spell discharges. If the attack misses, you are still holding the charge.Emphasis mine.
Basically, you have two options: touch allies as a standard action (no roll necessary) or strike as normal with an unarmed attack (not a melee touch attack). I had always played it such that you simply held your melee touch attack until later and got to target touch AC on a held charge. It seems to quite not be the case. Interesting.
You can " I had always played it such that you simply held your melee touch attack until later and got to target touch AC on a held charge. It seems to quite not be the case."
"Holding the Charge: If you don't discharge the spell in the round when you cast the spell, you can hold the charge indefinitely. You can continue to make touch attacks round after round."
The alternatively part it is an option.
The part about the "you may make a normal unarmed attack (or an attack with a natural weapon) while holding a charge." is if you have a claw and want to attack with it or a monk you can but it is not a touch attack but a normal attack that also have the spell.
From core rule book:
"“Armed” Unarmed Attacks: Sometimes a character's or creature's unarmed attack counts as an armed attack. A monk, a character with the Improved Unarmed Strike feat, a spellcaster delivering a touch attack spell, and a creature with natural physical weapons all count as being armed (see natural attacks)."
But the context for that quote is attacks of opportunity, not "what is a weapon".
The issue seems to be whether Touch Attack Spells are "Weapons". They are certainly "armed attacks". But are all "armed attacks" considered weapons? At first glance, they would seem to be. They require an attack roll. They can add in Sneak Attack damage. But at the risk of being confusing, the comparison stops short of calling them "weapons".
It's like the distinction between being Flat-footed and Losing Dex Bonus (if any) to AC. At first glance they both seem to be saying the same thing...but they actually differ quite subtly. Similarly, making an "armed attack" means you are threatening the space around you with a melee attack and you don't provoke an AoO when you attack with it. If my hand is crackling with energy, you're probably wise not to do something that will allow me a free attempt to touch you with it. On the reverse side, though, if I have a loaded crossbow in my hands (i.e. a "weapon"), I'm not threatening and you're free to dance around me as you like....even though my +5 supped up crossbow of death is the most dangerous weapon on the battlefield. And if I use it to shoot you, you get a free attack on me. So "weapons" and "armed attacks" are not always the same thing.
SKR specifically points out Rays and spells that offer the text "sword" or "sword-like" or "weapon-like" in their effects line to be weapons (even though Ray's are not considered "armed attacks" and you can't threaten with them). Touch attack spells, however, don't have effects lines. They have targets. So there seems to be a very subtle, yet important, distinction there.
Maybe the spell is just the rider on the Touch. A Touch deals no damage, so there is nothing for Vital Strike to multiply. This is the case in every example. The Touch is the same each time. What differs is the rider between the various spells and caster levels. But as a last note, I came into this discussion really REALLY hoping that Touch spells could be used with Vital Strike. It seemed to make sense and I'd probably still allow it in my games by saying that if you can Sneak with it, you can Vital Strike with it. But as I look at the RAW, this doesn't seem to be the case. :(
Honestly, if for no other reason than it would make maguses even more powerful than they already are vital strike shouldn't work with spells unless they specified as weapons or weapon like. Rays have that quality (but spells as a whole generally do not) and certain specific spells create weapons or are weapon like, such as flame blade. It would make sense to allow vital strike to funciton with something like flame blade. If there happen to be any rays spells were you can hold the charge (don't believe such exists) then it would be compatible with Vital Strike as rays have been linked enough to being "weapons" to qualify, but since it's a standard aciton to cast the spell and you can't hold the charge it's moot as they're incompatible due to aciton economy.
Well, riddle me this: I want to vital strike with vampiric touch. At level 10, I do 10d6 dmg instead of 5d6 and gain that much in temp HP. Do you allow this to work? Do you think this is how it should work? Forget empower spell. Let's just take vital strike.
Oooh, better yet. An 80d6 disintegrate at level 20, every round that you have spells, no metamagic. RAW, right?
Well, riddle me this: I want to vital strike with vampiric touch. At level 10, I do 10d6 dmg instead of 5d6 and gain that much in temp HP. Do you allow this to work? Do you think this is how it should work? Forget empower spell. Let's just take vital strike.
Oooh, better yet. An 80d6 disintegrate at level 20, every round that you have spells, no metamagic. RAW, right?
Rod of Withering?
Well, riddle me this: I want to vital strike with vampiric touch. At level 10, I do 10d6 dmg instead of 5d6 and gain that much in temp HP. Do you allow this to work? Do you think this is how it should work? Forget empower spell. Let's just take vital strike.
Oooh, better yet. An 80d6 disintegrate at level 20, every round that you have spells, no metamagic. RAW, right?
I certainly wouldn't.
Vampiric Touch is not weapon like and therefore couldn't be combined. Disintegrate is a ray, which makes it weapon like, but it cannot be held so it cannot be combined with Vital Strike due to action economy.
You're doing a great job of clealry illustrating why you shouldn't allow Vital Strike to work with many spells, and thats it not just a problem that would exist with magi.
Rod of Withering?
What about it?