Thanks, Valygrl and Dfege! This is giving us all kinds of ideas. Dfege, I'll be emailing you soon. We will be going self-contained, and camping out--stealth and campgrounds are always preferred, although we will consider a B&B or motel if necessary. We will be touring with our fine hound, however, so that complicates things.
I've been playing with some mapping software and looking over the hostel route. That stretch on the hostel route from Salton City up to Banning doesn't look so good, so staying in the mountains and dropping down into Hemmet more directly looks more appealing. Also, that would likely avoid what sounds like pretty predictable and severe headwinds getting out of that valley.
Basically, we'd like to do something like the hostel route, a big loop starting and ending in San Diego that takes the best of the best roads, light traffic, scenic with good camping.