But the reason the Bay area is so expensive is because Apple, Google, Facebook and 246 other Nasdaq-traded companies all call it home. It's ridiculous, if only for disaster planning. One natural disaster away from wiping out $3tn. Sitting on a fault line, no less.
So, yes, you could spend hundreds of billions hacking out better infrastructure links into this mess, or raise the speed limit, and that will increase "mobility". But that quickly translates into higher house prices even further out, and crappy new stock as developers get greedy. It's a vicious cycle that we've been over again and again and again, in many major cities.
Hotspots are toxic national planning mistakes that should have been smothered and forced out before they reached critical mass. Instead local pride (and land ownership) fosters them. Instead of fixing the problem, we're just trying to find new ways to make better returns on real estate investments. It's not sustainable.