They should rename "Guild Houses" to Premium Houses (because you have to pay 4.99 for them)
Then they should make houses around the same size that come with guilds when you buy a guild and anybody in the guild can enter it by default.
Then there should be a power that leaders can give members to "Edit guild house" so that members can add and remove their own furniture to the guild house, if the leader trusts the member enough to do that.
As people have mentioned before, for "Premium" houses, their should be a "Premium House" with a practice guild spar in it.