Hotel Cheval in Paso Robles might be worth a look? Stayed there a couple years ago and while it's not up there with Aman service or anything, the rooms - especially the larger ones - are pleasant, it's walking distance to lots of tasting rooms, and (at least back then) there are some nice touches like the option of being brought to your chosen restaurant in a carriage drawn by the resident horse, Chester

Agree 4S in Santa Barbara, Auberge Carmel and Post Ranch Inn all great options for when you're further south/north.