Funny, I actually live in Napa. So unless you're going up and then down again, you'll have to go over the 80 at some point. March could be just as bad as now regarding the snow going over Donner's pass. I assume you're go from SLO to here, and taking the 101 is slow, but prettier (and more cops, be careful in King County). From the 101 take the 680 to the 12 to Hwy 29. You might get other directions from Google, but that's the easiest less traffic jammed route. Be careful about the times you're driving. Google maps (at least out here) has pretty reliable real time traffic maps if you use your smartphone.
And there are things to do here that don't involve wine. The vines are all dormant, but it's still pretty if you do a driving tour. Napa is more expensive than you're used to, but you pay for what you get, mostly. So when you go to the Oxbow and pay $15 for 9 chocolates, it's totally worth it (and do go to the Oxbow). If you're into wine, there are some places here that you can still get free tastings *if* you're a local. There are a couple places to hike. The touristy areas are more up valley, but the city of Napa is actually getting some more things to do. Definitely go into San Francisco!!! It's really a wonderful city. It's about an hour away. There are some cool, free things to do in the bay area, but you have to go during the week to not be totally bombarded with other tourists (like Muir Woods).
And if you're thinking about living here at all, the rent and cost of living is high, but what you get paid makes up for it.