The one downside to matt's idea that is glaringly obvious to me is that the new buffs would have to be insignificant enough to not encourage the formation of uber guilds. Also, one city per level would probably encourage servers to have two at most 3 notable guilds. I doubt half a dozen guilds would want to be participating in a bidding war over a single city, on some of the more active newer servers the bids can already get into the thousands and thats for the level 3 cities.