I feel that simply raising stats for higher difficulties is a very poor way to raise the difficulty of quests. I feel that enemy casters should be more intelligent about using their class abilities, i.e. spells, and buff up before adventurers get within sight of them.
I'm not saying that all enemy arcane casters should have all of the arcane buffs active, but they should have *some* buffs appropriate to their level.
Oh, and remove false life from enemy casters' spell lists. False life only gives a small amount of temporary HP, and it's all gone in one hit. How about Protection From Energy? Or Nightshield? Those are worthwhile, and may make it a good idea for casters to use dispel effects.