Gentrification is a real social concern that needs careful but focused solutions
Not really: Up until the Petaluma City Plan was found legal in the 1970s (see http://en.wikipedia.org/wiki/Petaluma,_California#History for more) and the growth of height-limit acts in major cities, places that experienced growth built more buildings to accommodate new residents, so prices stayed (relatively) low for most people moving to a given locale.
We're seeing the end game of extreme supply restrictions in popular major urban areas: very high prices as increasing demand hits limited supply. The solution is to increase supply, but SF has mostly chosen not to do this: http://www.theatlanticcities.com/housing/2013/10/san-francis... .