I take CalTrain to work most days, and it is sort of good enough. If and when they electrify it and replace the rolling stock with EMU cars, that'll make it that much better. My nephew goes to U.C. Berkeley, though, so he lives in BART country. There's been moves afoot for a while to bring BART to the South Bay, but I think I've decided that a much better idea would be to run VTA light rail up to Warm Springs, where the current planned terminus of BART is.
BART is a broad gauge rail system that because of it's third rail electrification must be totally grade separated and fenced in. Light rail, by contrast, is standard gauge rail with overhead electrification and hence has no need to be fully grade separated. In fact, there's no inherent reason that the line couldn't be shared with freight service.
The proposed BART extension to Warm Springs is already on track (see what I did there?) for construction any time now. The proposed location of the Warm Springs station is a mere 6 miles away from the Great Maill VTA station, and there is a railroad right-of-way that actually connects those two locations!
You don't need to tell me twice that the government's involved when the plan is to spend billions of dollars to run BART 15 miles to downtown San Jose (including tunneling under it) and thence to Santa Clara when all they really need to do is go 6 miles further than they're already planning on going and just stop. But even then, just electrifying the 6 miles of track between those two stations and running VTA trains up and down to meet up with BART would probably be cheaper still. If you ask me, it's entirely unreasonable not to connect these two systems together by adding a small extension spur from the Great Mall station to the Warm Springs station, turning it into an intermodal station.