If low density is why San Jose can't support a decent transit infrastructure, then how can Denver do it with even less density?
Silicon Valley office space seems to be a little more spread out. When I was visiting a client in Santa Clara last year, I had to walk almost two miles to get to a light rail station to go have a nice dinner in downtown Mountain View. (And there were no buses available to cover that distance -- at least not that Google Transit knew about.)
(Disclaimer: My experience with San Jose is mostly limited to the airport area, and the Silicon Valley suburbs to the north.)
I share your enthusiasm for the upcoming expansions, in particular the line to the Airport. The train is one of the big perks of living in Denver. It's awesome and only getting better.