Okay, filtering out all of the mediocre items and altars lets you set up some amazing combos.
I just played a game using a rogue and taking the scout altar and bank preparations. I bee lined for the first altar and found Binlor. I sacrificed about a 1/3 of the map to gain 150 piety from him (used the resistance-reducing boon 5 times). You can mitigate the cost by using ENDISWAL to burrow into otherwise unreachable tiles. If I had found a nice subdungeon, it would have been even easier. I then converted to Glowing Guardian, starting me out with 50 piety.
All of the early map exploration revealed tons of powerups and shops, including one selling the agnostic collar. I bought that, and then desecrated both Binlor and Taurog, giving me 100 piety in total and letting me get Enlightenment at level one! I didn't even need the collar, since I could have desecrated Binlor without it and I had found plenty of garbage glyphs to convert anyway. By level 5 (post-humility) I had about ~80 piety again. At that point I could just ignore GG's complaints about potion use.
If the third altar had been Dracul instead of Taurog, it would have been nuts. By level 5 or 6, I could have used Absolution to gains tons of hit points, convert to Dracul, and then have access to Blood Shield and still have tons of piety left over for Blood Swell. The synergy between Absolution, Enlightenment, Blood Shield and Blood Swell is just crazy.
I also think I could have easily gotten away with using Binlor's boon 10 times instead of 5, which would have been amazing.
I can't even imagine what a Crusader could pull off with 4 altars.
I still haven't found the Earthmother. Would she fit into this scheme? I'm starting to regret unlocking Taurog, to be honest.