Take a look at the current VTA route map for that area: [www.vta.org]

Bus lines serving the Campbell-Los Gats corridor from the current end of the light rail (Winchester station) are the 48 and 49. Given the wandering route (common with bus lines that have to serve both local and regional service on the same line) it probably takes at least 1/2 hour probably closer to an hour to get from Los Gatos to the station. Neither line is probably very productive, though if you add up all the runs for the day you can probably come up with the 200 projected for the LR extension, or even a tad more, but many of those will be local trips. If people are going someplace outside the local area, they drive.

Extending the line might get only 200 riders a day. I think it'll do better IFF VTA rearranges the buses to adequately feed the stations. People will put up with a well-coordinated transfer, and with all its faults the train is more direct and faster than the wandering bus. OTOH, adding HOV lanes to 17 and running express buses there would stomp light rail prospects into dust, while improving things for a lot of people who would see a slight reduction in congestion, at probably a similar cost per mile. But the local pols like their trolleys...

BTW, original estimates for Folsom light rail service on Sac RT were on the order of 300 riders per rush hour (not per train) each way, with a few others scattered through the day. That was the number of people the express buses and FTB shuttles handled. Even after the luster has worn off, it's more like 200/train in peak hours (just from Folsom) and 50+/(shorter) train off-peak. We grumble about the uncomfortable, dirty seats; the afternoon 'floor show'; and the constant stops -- but we use it because it fits our travel needs at a much lower overall cost than driving. And we make more space for the SUV/monster pickup drivers on 50 which they should be happy about. Which is just roundabout justification for saying that the 200/day number for the Vasona extension is probably lowballed if VTA can fix up connections properly or provide adequate parking.