Gentrification is not caused by 'a few hipsters'. They're just an easy target. When you get areas 'improve' through an influx of more wealthy people, it's not just baristas with sleeve tattoos. But general professional staff of all races, young families, etc..
If you live in a city with high house prices, new home buyers will look to move to affordable areas. Which in time, will improves the standing of the area.
Gentrification is an inevitable aspect of population growth and housing markets.
Basically this is what it boils down to. There are hipsters, rich people and professionals trying to find housing, but what Spike Lee might see as some cultural invasion is really coming down to population growth at its most fundamental level.
This happens in many poorer neighborhoods. Artsie people move in due to low rent, then demand of the area increases due to it being hip. Then the artsie people leave the area because they can't afford living there anymore, and you are left with rich people living in a neighborhood that lost its coolness factor. At some point I assume the rich people will leave the neighborhood, demand will decrease, and the cycle will continue.
To a degree, but remember that there aren't constants in that equation. At least in the US, we're going to have a robustly booming population for the foreseeable future. So it's more likely things are going to get pricier rather than crash, absent some drastic stuff that decimates neighborhoods for decades (and I don't think we want or need more race riots.)