I didn't mean to imply that you should just give everybody awesome bonuses. I just mean that if somebody wants to abuse something they're going to, amazing bonuses or not. I think the current monster classes are actually really good.
For the half fiend, would it be a problem if, when multiclassing, it could add to levels of Wizard instead? Same goes for a lot of the other monsters that give spellcasting bonuses if you multiclass to Sorcerer.
Maybe this is unbalanced. I don't know, I'm just throwing things out there.