So you're comfortable letting a 12th level character throw out a 48d6 touch attack?
So you're comfortable letting a 12th level character throw out a 48d6 touch attack?
At 12th level? Sure. Hitting isn't the problem barring improved cover, all else being equal. Concealment, vision, displacement and the save DC are all some of the factors contributing to making it far from guaranteed on the ability to deliver that failed save damage.
A simple mirror image makes it almost-guaranteed useless unless they're burning a LOT of gp and precious 6th level spell slots on true seeing over the course of their career. Some players are notoriously stingy about spending gp on M components, so they'll lose a round or two just getting their bypass spells into play.
You can't disintegrate what you can't see. You can't critical hit if it benefits from concealment. Both are common tactical challenges at 12th+ level play - and have been in many campaigns since 1st level.
I'm also just as comfortable with a monster doing the exact same thing to the characters. This isn't a player-exclusive thing. *grin*
Edit: having said all of that ...
The better design re: Vital Strike and company would have been to bake them in as a combat option as part and parcel of gaining improved base attack bonus and the accompanying iterative attacks. Either (a) full attack multiple times via iteratives as normal; or (b) one attack with improved base weapon damage dice a la Vital Strike et al. This would eliminate Vital Strike as both a feat and as an option for higher-powered spell attacks such as shocking grasp, disintegrate and so forth. There are a few weapon-spells e.g. flame blade, force sword and instant weapon that create a weapon. For those the combat option to iterative attack/Vital Strike chain works just as well as it does for those wielding regular weapons.