My recollection is that Enterprise does not charge an extra fee for one-way rentals within California, but that they only do one-way rentals from airport locations. My partner and I managed to get a free upgrade to a convertible at Enterprise (from mid-size) when we were going from LA to SF and decided to take the PCH up as a result. I would not recommend doing the PCH for such a long stretch. It is beautiful, but gets tiring, and for large chunks of it, you can't really change your mind and get back to a freeway. The recommendation to break off at SLO is a good one because I think you should go see Big Sur. I might have missed this in an earlier comment, but if not, Sierra Mar at Post Ranch Inn is highly recommended -- try to go during sunset.

I've managed to get reservations to French Laundry twice. If you get a couple people to call, you can generally do it, but yes, it has to be two months in advance, and it's easier on week nights. Since you've got a decent break, maybe plan for a week night. I too have heard good things about Cyrus, but haven't been. My favorite non-FL meal in Napa was Redd.

In the SD area, I love Coronado. This might be cheesy, but I also love the Wild Animal park.