How cool would it be if we could put unique items into temples as relics?
And the higher the prestige, the higher the religious draw?
Then people would have a strong incentive to loot temples, too. To get ahold of those sweet, sweet relics, and put them in your own temple. This might also get to the point where temples (at least in smaller regions) might be gold-positive (or at least neutral), because the extra pull of a high-prestige item might attract enough followers to make up the difference.
Or, if that is not a desired result, maybe instead of drawing more followers, it enhances the fervour of the followers, so they provide stronger buffs when lords of their religion are present, and stronger debuffs if not. That would also provoke more conflict, as a heathen lord might be incentivized to take the relic to stop the faithful of the region from continually agitating against them...At the cost of a religious incident.
