Lots of good suggestions above on food and walks in SF. I'd add the Crissy Field walk out to Fort Point for great views of the Golden Gate, sailboats, and of course The Bridge. You can hike up the hill and walk across the Bridge if you want.
I'll address the day in the country/wineries part of your question. If you're looking for smaller wineries w/ a less touristy feel, I would avoid the Napa Valley entirely and head in one of four directions:
(1) Sonoma County/Anderson Valley. This will be a long day trip, but it may be worth the drive. The Anderson Valley is west of Hwy 101 and close to the coast, so the weather is cooler and wineries there have excellent success with varieties such as Pinot Noir, rieslings, gewurztraminer, as well as sparkling wines. I've been buying wine for years from Navarro Vineyards. (An alternative to the Anderson Valley, and less of a trek, is the Sonoma Co area around Calistoga and Geyserville, but I'm less familiar with the wineries there).
(2) Amador County/Plymouth: In the Sierra foothills. Small wineries doing very interesting things with Rhone-style, Italian, and Spanish varietals (e.g., Tempranillo, Syrah, Albarino, Viognier, Barbera). A lot of the wineries up above Plymouth are small-scale, family run operations, much like the Napa Valley was in the 1960s and '70s but is no longer. Buy picnic fixings at the Plymouth Market and then head up to the "Shenandoah Valley" to visit the wineries there.
(3) Calaveras County/Murphys: Also in the Sierra foothills. Less well established than the Amador Co wine region but expanding rapidly and interesting things happening, again with varietals associated with Spain, Italy, and the south of France. I strongly recommend Hovey Winery, which opened a tasting room on Main Street in Murphys about a year ago. There are also good places to eat in Murphys (I recommend Mineral, and Alchemy).
(4) I am not that familiar with the wineries of the Santa Cruz mountains south of San Francisco, but if you don't want to do a lot of driving I strongly recommend going to Ridge, on Montebello Road in Cupertino. Spectucular location. Legendary wines.
I understand and sympathize w/ your desire to avoid big in-your-face (and high alcohol level) wines. I've been complaining about this trend in California winemaking for a number of years. It's hard to avoid them entirely, however, since the hot, dry climate in many wine growing areas tends to concentrate sugars in the grapes. But you can find wineries that produce wines with finesse and subtlety. I'd suggest picking a destination spot for your day trip and then reading up on the producers there. Enjoy!
