Agree with David that 29 isn't much fun; I've done it in the opposite direction. It's a multi-lane road with high-speed traffic and not a great shoulder. On the other hand, to get there you can take the ferry to Vallejo, which is fun (at least in my opinion). I haven't ridden all of that stretch of 121 and 128, but the parts I've ridden are nice - low traffic, slightly windy country roads. You might have to deal with boat trailers on their way to Lake Berryessa, though, and that too isn't fun, since those roads don't leave a lot of space to be passed by a wide trailer.
You can also Amtrak from Oakland or Richmond to Fairfield (or Martinez), if you want to shorten the ride.
Nathan