A heroic victory condition could be interesting. And certainly fits with the theme.
I'm going for a tower of magic victory now. There is not a lot of suspense. Especially if you are waiting until Fire to focus on the end game, my suggestion would be to simply reduce the amount of time it takes to build the tower of mastery. I'm basically just playing now so that I have a sense of completion. I'm building strength 15 units to defend my borders against straight 6 units.
That said, while I was trying to get the Mana, it was great. It involved conquest, but not blind conquest. I was fighting for strategic control of resources -- much more interesting. And I played on the "Continents" map, which meant there was a new world to go explore and take the Mana from. All in all, I'm happy with the victory condition and just think it needs some tweeking.
I was playing on a large map and I have to say it was a lot better than domination/conquest. I've never felt it worth to go through the trouble of one of those victories on a larger map.
I like the idea of religion specific victories.
PS: I just switched to Ashen Veil for the first time. Awesome graphics.