Riverside, San Diego, and even Los Angeles county have a number of mixed terrain riding opportunities (including gravel) - I'm not aware of anything similar in the OC, but then I don't ride there frequently.
I'm curious what you are expecting to get out of a Vaya or Casseroll that you couldn't get from your Cross Check?
While I haven't tried the Vaya, I own an '09 Casseroll (triple) and have put ~10,000 miles on it since last year. It's a great commuter and a pretty good rando/distance bike. The acceleration isn't ideal for fast club rides, and the weight will bog you down a little bit in the mountains - though if you've got the engine, it will do in a pinch. I've ignored Salsa's advice (the fork wasn't designed for the stress? I think this has been corrected with the '11 version) and taken it off-road many times, even including some single track. In the future, I'll probably put some Small Block 8 tires on for this kind of thing rather than trash my slicks (28mm Schwalbe Ultremo R.1) or shorten the lifespan of my commuter (27mm Ruffy Tuffy) tires...on the other hand, if/when I do the
Dirty Kanza or
Trans-Iowa, I'd prefer a dedicated cross/monster-cross/gravel-grinder bike for the task.