I'm thinking that houses would fall into designated groups, such as New Player House, which would range from the Starter Hut to the Woodland Bungalow. Midgame House, which would range from European Lakeside to Designer Two Story. And Endgame House, which is the rest of the houses.

As for the issue of people switching between houses to see different markets, that's a good point. I'd say it's quite a hassle to move out of one's current house just to see a different market, so I'm confident that most players wouldn't bother...but of course, there's always that one person. ^^; Perhaps there could be a strict house cap, like two houses per player, to discourage that behavior. Or, the house groups could be programmed so that once you advance to the next group, you can't see a "lower" market even if you switch houses.