I don't want to sound callous but ... market forces shape and reshape cities all the time. When the facets of city-life in San Francisco that initially drew people fade away, people will flock somewhere else and the rents will stagnate or reverse. And if San Francisco is losing its allure as an artist's hub, perhaps other places (such as downtown Detroit) are compensating? I live in a reasonably affluent smaller city…
The only people who are really concerned about this are the ones to insist that SF and Oakland are totally different cities. Come on guys, they've been the same economic region for 100+ years, it's time to admit that they're the same city.