I've heard the theory that high-end housing still creates opportunities for lower-end housing. If a desirable neighborhood gets new expensive units, that means

I've heard the theory that high-end housing still creates opportunities for lower-end housing. If a desirable neighborhood gets new expensive units, that means (1) some residents who now earn more than when they first came can "upgrade", leaving their older and cheaper units open, and (2) people who can only afford the older units don't need to compete as much with wealthier buyers.