If you want to preserve old buildings, buy them and hold on to them. Prices depends on supply and demand: if you reduce the supply of something and hold demand constant or increase it, that thing becomes valuable. The problem with preserving "old" buildings through legal means it that doing so prevents new supply (which usually means "more units for an acre of land") from coming online, thus increasing housing costs altogether. See: http://www.theatlantic.com/magazine/archive/2007/11/a-tale-o... and http://www.amazon.com/Gated-City-Kindle-Single-ebook/dp/B005... for more.

I regret not being able to live in places like Boston and L.A. because poorly conceived preservation laws remove building rights from owners and prevent them from constructing dwellings I and many others might actually be able to afford.