Hm. Scion of Purple ribbons would make even more sense at P'con, now that you mention it. (Not that I make it to P'con every year, as it's even more about socializing and less about subject matter than the other cons I attend. But I can certainly day-trip it.)

And while BART doesn't come directly to BayCon's new site, you can pick up any of the VTA lines that come up to Fremont, and transfer to light rail once you make it to downtown SJ. I know that's still time-intensive, and suboptimal if you're traveling with luggage, but there are at least options.