Monkeygrinder's Organ
Dodgy geezer swilling vapid lager
In the context of fully marketised housing provision - something we're still far from, but moving towards - the distinction between things that regenerate an area and those that gentrify it is virtually meaningless. In this context, having an open Post Office rather than a closed-down one, or having less street crime are gentrification, because anything that makes an area more attractive to live in will increase the amount that can be charged for housing and so determine who can live there.
I think this is true. The other thing is that, for the same reasons, it's not really caused by people acting badly. Ultimately anyone who can afford to pay more than someone else for housing is pushing prices up to some degree, and you don't need to be a hipster, a Claphamite or even a particularly rich person, for that to be the case.