Mind = Higher MP, Higher Cures.
Intelligence = More Damage from spells.
Piety = Duration of spells(IE: Burn, Blind, Paralyze.), and less resistance(Magic Accuracy)

As of right now I have noticed equips do not add MP via Mind; Only base mind will add MP.

I am unaware of anything else that is gimped due to equips atm. But anyway Piety vs Magic accuracy..

I feel Piety is the better trait because accuracy will only help on resistance, I do not think accuracy affect duration. I am both 50 THM and 50 CNJ my DoM stat base is as follows;
Strength: 12
Vitality: 65
Dexterity: 15
Intelligence: 122
Mind: 115
Piety: 109
As far as equips go you have to have a different set for each of the following tasks:
Healing, Enfeebling/Backup Heals, and DD. I have not really encountered too much problems with being resisted. Also you can use Purge to render the enemy neutral to all elements. At this point almost all Enfeebling spells will land effectively.