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If your neighbor subdivides their lot, the smartest thing for you to do is subdivide yours (after all, it will turn your $1M into $2.5M, no?)No, it doesn't. Subdividing and building more houses on it turns it into $2.5M.
Most people will not have the cash or financing available to do that. And many people who want to do this will likely spend years doing it. And many people, even seeing their neighbors do it, just won't want to. They perhaps like the size of their lot, or don't have any family or friends that they really want to live that close to.
> last house in the neighborhood full of subdivisions will have the lowest sale value (and the first house to subdivide will be the most valuable).
If true, so what? As long as its sale value is more than it cost to build, that's fine.
> By "rapidly" I mean on the span of a few years.
That just isn't going to happen. GP's estimate of several decades is much more likely.
> the system needs a moderating factor to prevent runaway.
I don't think there's really any risk of that happening. At any rate, the problem is that we don't have enough housing; increasing the number of houses, and making them more affordable, is the entire point here.