There are lots of venue possibilities in the Bay Area, as mentioned. To summarize some factors to consider:
1. Schedule around a date when the UK Empeg people will be in town
2. Keep the distance to within ~1 hour drive from Sonic Blue in Santa Clara
3. Select a place to eat that can easily handle all the expected attendees and has (or is near) a large open (free) parking lot
4. Try to schedule it on a non-holiday/non-special event weekend to avoid crowds and hotel issues for out-of-towners
5. Give people at least a month to make plans

Also, some place that is relatively easy for people to find and is in a nice setting would be good.

Loren, skritch and others have already made some good suggestions. Here's one more:
Roaring Camp in the Santa Cruz mountains; nice setting, open eating, big parking lot...and a real choo-choo train!

Barry