Three tiers of religious area, the first being an altar with an AoE of three tiles. Simply, the altar would give 100% success rate when using one of the Piety skills. The Temple could grant a 30% additional luck or one of the God's buffs. The church would increase it to 50%. All three would allow for 100% success rate of the piety skill, and perhaps give a lower durability degradation for buildings within X amount of tiles if said tiles are within a claim.
Outside of those buffs, I also think it'd allow some room for RP-ers to do things as well, and would offer just another nice niche to the game.