1) Auto-abandon of unpaid houses more than 12 months behind on maintenance. This should only be done if escrow will be unlimited and allow for a player to come back three years later and still have their stuff, but not their home. If this is done, then they'll be able to buy a new house pretty easily, because those who aren't using them are constantly recycling their homes back into the pool. All they'll lose is the layout of their stuff, which is a tiny price considering the fact that they haven't played in a significant amount of time.
2) Assuming #1 is done, we should consolidate all of those neighborhoods which will now have a lot of empty houses. As long as I don't lose my address, I don't care which neighborhood instance I'm in, and would much prefer to have some real, breathing neighbors than be in an empty instance.
3) Meaningful content inside of neighborhoods. Something similar to festivals should occur in neighborhoods. Imagine horse races with your neighbors, or dancing around the party tree. Another idea is to have an evil influence arrive in your neighborhood due to the Enemy's machinations. You have to complete some quests to investigate the situation, or else your neighborhood will be dark and dreary and evil creatures would occasionally attack you in the neighborhood common areas. This would all have to scale to level of course.
4) Something better than the current hook system. This has been explained enough by other people.
5) A "dressing room" option for housing items. I'm tired of being disappointed by what an item looks like after it is placed.