I'm wondering if a mage build needs Perception and Dexterity to land spells more often. How about DD spells? And more importantly how about illusion, charming, psychic attacks, healing or bard skills?

For pure Intelligence based, targeted DD spells it might make sense. For psychic, charm and illusion spells (magic schools governed by Int + Charisma) it makes a lot less sense. For summoning or bard spells it makes no sense at all. And it would be a problem for making efficient charisma-based magic builds, as one would need Int + Cha + Perc + Dex to be efficient (with very little health as a result).

If Perception and Dex are the basis for hit rates (accuracy) of all types of attacks (melee, archery/ranged and magic), then marksmen and assassins would clearly have a huge advantage, as these are their school-governing attributes anyway. They could then easily stack health (Con) and mana (Int) on top, while the charming mage would have to live with minimum health and carrying capacity.

Finally a related question: is evasion (Dex) also affecting spells?

I'm pretty sure Mages need perception (for accuracy and crit) and dex (for accuracy and evasion). So contrary to the OP's impression mages are actually at a disadvantage, requiring Int + Perc + Dex (and possibly Charisma). And everyone needs some Constitution, so Mages end up jack of all trades much more than e.g. Marksmen or sins.

I'm pretty sure Mages need perception (for accuracy and crit) and dex (for accuracy and evasion). So contrary to the OP's impression mages are actually at a disadvantage, requiring Int + Perc + Dex (and possibly Charisma). And everyone needs some Constitution, so Mages end up jack of all trades much more than e.g. Marksmen or sins.

Thanks for all the answers, gave me some new perspectives. They seem to be a bit contradictory, so it might all be more complex than expected.

If the higher skill (of perception or dex) has relatively more impact on accuracy (as @TheRipperOne suggests) it would be better to go 18 Perception for the extra accuracy bonus. If most spells do not depend on accuracy (as @Jetah suggests) a mage could skip Perception and take Dex 18 for the evasion bonus (or none of them, going for e.g. Con). Who knows, anything is a good guess at the moment.

There is no mention anywhere of a separate physical vs. magic accuracy, so I do not agree with @muker on that.

Charisma mages might be very strong against chars with charisma 6 (something many melee and archery chars will probably use), on that I do agree.

Still, Perception looks like an uber skill for every build, heavily influencing such important stats as accuracy, critical hit, gathering, identification of items etc. (+ assassination & marksman). In comparison Strength and Charisma are much more constricted to specific builds (melee, illusionist, bard or summoner). On the other hand, Int is also a must for basically any build.

I'm wondering if a mage build needs Perception and Dexterity to land spells more often. How about DD spells? And more importantly how about illusion, charming, psychic attacks, healing or bard skills?

For pure Intelligence based, targeted DD spells it might make sense. For psychic, charm and illusion spells (magic schools governed by Int + Charisma) it makes a lot less sense. For summoning or bard spells it makes no sense at all. And it would be a problem for making efficient charisma-based magic builds, as one would need Int + Cha + Perc + Dex to be efficient (with very little health as a result).

If Perception and Dex are the basis for hit rates (accuracy) of all types of attacks (melee, archery/ranged and magic), then marksmen and assassins would clearly have a huge advantage, as these are their school-governing attributes anyway. They could then easily stack health (Con) and mana (Int) on top, while the charming mage would have to live with minimum health and carrying capacity.

Finally a related question: is evasion (Dex) also affecting spells?