NOH2O,
If you stay in SF, you can reach Napa and Sonoma counties with ease in about an hour or so depending on traffic. I would only recommend the wine train if you want somone else to think for you. You end up on a train in parallel with the highway and are "captive". For me, I would rather get out and see some places and linger when you find a great spot. You can PM me for suggestions, I just spent 3 years up there.
Monterey is a nice day trip and more relaxing than SF (my opinion) and can make for a nice weekend as well, after that and you may be looking for more to do???
One thing to note is that Monterey county has a pretty strong wine industry as well, so you could knock out golfing, wine and a romantic place all at once
Hope you have a great trip!!!!
-Chris