Sieges should have some kind of impact on the town being sieged. Vendors should close up shop and refuse to buy or sell goods. (yes, including player vendors) Teleportation should no longer take you inside the town, you should instead be teleported into the seige camp area. Devotionals should not work during a siege. The longer a siege lasts without being lifted should matter. End the siege quickly, you should get a bonus. Have it last for a long time, perhaps your town gets a debuff for an extended period of time. EDIT: When a player or group helps lift a siege. Their names should be spoken favorably by the NPC's in the town, and this should help the virtue of the players.