I'm skeptical about piety since the cures' MP costs scale with your level. To me it makes more sense to make cure more potent so as to be more MP efficient. Of course, you have to watch overhealing, but if you watch the HP bars and have a general idea as to how much each cure spell will heal, (crits notwithstanding) it evens out to save more MP for me that way. Especially when Freecure procs.

But I only got CNJ to Brayflox in the beta and haven't reattained that yet (can't log in XD), so that may change later for all I know.