If you're into Glashutte Original and want to actually see them in the flesh, Topper Jewellers are in Burlingame, just outside SF- near the airport. They're good guys.
Not sure about used watches.
We've done that trip a few times. It's a great part of the world, especially when you get north of Santa Barbara - the traffic thins out and the views get prettier. San Simeon is worth a look (plus there's a beach where the Elephant Seals congregate just north of it), then Carmel, the 17-mile drive and Monterey are worth a detour on your way back to SF.