I, as well, think 2 weeks is a fair amount of time -- though you might get tired of the driving.
Napa/Sonoma should be fine that time of year. Not as pretty as in the Spring, but it will be fine.
Maybe start in SF and end in SD?
And as I live off the 101, I agree that the 101 is much more scenic; you also get a better idea of the state since you can drive through many of the larger cities (Santa Barbara, Thousand Oaks, San Luis Obispo, etc.).
You might want to get a Fodor's travel guide as it lists different side trips you can take around the state.