Now that I think about it, I haven't really given too much thought on Bard attributes.

I'm wondering if the abilities that gradually restore MP or gradually increase TP will count as healing magic potency or enhancing magic potency (if they count at all).

Or as you say, one of the two auto-attack governing stats, Dexterity and Piety, may be used to govern job ability effectiveness too. It would be great if it t'were Piety!