Well, I personally think that going to SLO would be worth it. But I'm biased, having spent a few years there while in college. It's a beautiful town, with a nice downtown (Thursday night farmer's market is not to be missed). You could always stay one night there, then drive to Hearst, leaving your luggage in the car there (I would think it would be fairly secure there given the amount of foot-traffic). Then you could stay a night in Cambria, or continue up ther coast and stay somewhere further north.
Another possibility, if you really want to leave your luggage at a hotel, would be to stay in Morro Bay. It's another nice town, and is about 15-20 minutes closer to Hearst, so the drive back there after getting a tour wouldn't be too bad.
But again, if I were you I would go to SLO, spend a day there, get a nice hotel (Madonna Inn, of course, is an experience in and of itself), then check out, go to Hearst, and continue a bit further north and stay at a hotel there.
As I recall there are a couple good threads on the CA forum regarding Hearst Castle, San Luis Obispo, and the drive up/down 1. A search would probably reveal more input/thoughts.
Good luck, and enjoy the trip!