Look, really, there isn't anyplace in the central part of the state that isn't drivable from any other part of the state. With airfares being what they are, the key to large attendance is picking a vaguely centralized location that lots can drive to.
Think Davis. Or Sacramento. Or Fresno. Or Bakersfield. Or Santa Barbara. or San Jose.
Then combine any of these city with a decent airport for out-of-staters, and ideally, a good museum or airshow on the same weekend, and then you have a perfect location for a west-coast mini-con. I've been to a San Jose Mini-Con in 2003 (for warbirds) and it was cheap, easy to plan for, and fun.
Anyone remember the 2000 Warbirds Cons? That's right - two cons at the same time. One was in Palm Springs, and one was in Washington DC. We had contests between the two cons, and it was a blast. Each had more than 100 guys attending.
-Llama