Very good questions to ask

The real question was whether low-income residents moved away from “gentrifying” neighborhoods at a higher rate than they did from nongentrifying neighborhoods.

That's from an excellent piece in Slate about the vagueness and questionable utility of the concept of gentrification. Of course the opposite of gentrification--neighborhoods that stagnate and decline--is a much bigger problem that doesn't always attract enough media attention. I agree with mostly everything in the article, although the idea of community value in neighborhoods not being priced into the property exchange markets doesn't really come up.