I feel I'm kinda in the same boat as the OP on this one. I'm only rank 14 CON and THM, but these abilities don't seem to be worth the AP cost to set, nor the stamina to use if they're going to wiff 60% of the time on mobs that matter, and only return a paltry amount of MP on the occasion they do connect. Perhaps they get better in time, or maybe I'm just missing something here.
What I've found works well for MP regeneration is to have both THM and CON leveled a bit, and leave both Exaltation and Tranquility in slots 29 and 30. Since they have no AP cost, you can leave them set there on any job without taking up space. This allows you to avoid the cooldown timer when changing to THM or CON, so you can swap between them to restore half your MP every 5 minutes instead of 10. For the moment, this provides more than enough MP to reduce any benefit from Damnation/Radiance.
Edit for stats: 43 INT, 52 MND, 51 PIE, 39 DEX, 50 VIT, 16 STR
Edited, Oct 26th 2010 8:38pm by FFSeij
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