Slate has an interesting article looking at gentrification and how it is in fact a very rare thing. That which we consider gentrification actually isn't, and the effects of bringing a neighborhood up in fact extends benefits to all those who live in it.
In the article, they find that there is "no evidence that poor people moved out of gentrifying neighborhoods at a higher than normal rate...; as neighborhoods gentrify, they also improve in many ways that may be as appreciated by their disadvantaged residents as by their more affluent ones," and, "the problem isn’t so much that gentrification hurts black neighborhoods; it’s that it too often bypasses them."
"Retiring the term gentrification won’t do anything to address these problems, of course. But it will remove a distraction. Let’s examine how neighborhoods really change and why some don’t. Let’s debate supply constraints (in addition to providing affordable housing) in the San Franciscos of America and figure out how to provide rent subsidies in the Rust Belt. It won’t be as fun as decrying or defending gentrification, but at least it will be directed at problems that are real."