To expand further why I think you haven't made a good argument: if high vacancy rates are the problem, and the Bay Area has especially low vacancy rates, why is the Bay Area the least affordable region in the US? High vacancy rates are obviously not the cause of the housing crisis. Maybe you can make the argument that high vacancy rates _coupled with something else_ is the problem, but you don't seem to be making that argument -- and the "something else" is probably the more important factor anyway, since SF doesn't have high vacancy rates.