I happened to get the Vanya hat of healing built and melded up yesterday for my white mage. You can't add any mind/vit/piety.

However, you can add +5 to the critical hit chance (went with a savage aim 3 in one of the 100% slots). I also capped the spell speed which goes up to +16. Went with quicktongue 3 in the other 100% slot, then two quicktongue 2, and lastly a quicktongue 1.