I live in one of those "Yuppie" buildings in Chinatown everyone complains about
I really enjoy living in the area though, it has great dining options and you can access basically any part of the city by either foot or T (walking distance to 4 different T lines). I also believe it is one of the most truly urban areas in Boston, you have so many different races and economic groups living and interacting on a daily basis. Safety wise my wife and I have had no issues at all and I also think that late at night it is one of the few areas where you have street traffic early into the morning.
As far as Chinatown turning "non-asian" I doubt it. The neighborhood is still over 75% Asian and I can personally think of at least 40 different restaurants and bakeries off the top of my head that are constantly filled on a nightly basis.