If you have Intellect, you can take the hit to the Will defense, if you are even concerned about it to begin with. The Deflection you get from leaving Resolve at 10 isn't going to save you from anything if you are otherwise squishy. I mean, do you want 7 deflection or +21% damage?

Resolve is a dump stat for Wizards for sure, since they have numerous self-buffs to compensate for it.

 

As for other casters, it depends. If you're like me and like having Druids and Priests participate in melee you probably don't want to dump Resolve. If you go ranged, you usually can dump it without too many repercussions. But it never hurts too much to have some Resolve, since it does affect your Concentration, and nothing sucks more then getting Interrupted a lot from DoT effects or ranged attacks.