When a house becomes available, start an auction period on it (1 week perhaps) where anyone can go up to the placard and place a bid. At the end of the auction the highest bid wins the plot and everyone else gets their money back. No incentive for buying low just to resell, a more powerful gil sink, and no having to pray that you get lucky and catch a vacant lot some day before it gets scooped up. I'm a little surprised that it doesn't work this way already.