I recommend that you stay as much as possible on the coastal route. There are any number of things to see and do out there -- too many to describe. If you can, and the conditions are right, you might want to consider the 'lost coast' in northern California. When I went there last the road down from Ferndale to the coast was a bit dodgy (in my low-slung Miata at least) but you will see things when you get to the coast that very few people ever do. Further down, the road cuts inland but there are a number of interesting roads leading back to the coast and some magnificent scenery. Ferndale itself has some interesting Victorian architecture if you are of a mind.