A good question limmer: I also don't see I do more magical damage (but not sure) ....
But I go for Intelligence because of the many enemies that attack with magic spell and if your Intelligence increased, also your Magical Resistance increase! And your Indomitable Will go higher too.
Your second question: Yes, Confusion is something that give you more time: it lower the offense because for a sort time an enemy is confused when you attack him with a magic spell! Each spell you use confused the enemy (Magic Missile, Magic Blast, Fireball,... I don't know if Confusion having influence at for example 'Firewall' - someone experienced this?).
The skill "Destruction" strengthen all your magical attacks and is like Confusion a passive skill, handy for doing more damage etc!
Success