Hiking in the vineyards
Sure, seeing a wine cellar is interesting--the first time, but unless you're there during harvest you don't really see that much. Several wineries are offering vineyard hikes now. As most winemakers say, "This is where the wine is really made." Best time to do this is probably April through September. Read about it in the Press Democrat.
Seeing the cellar during harvest
As far as actually getting into the cellar during harvest the only place I'm aware of that does this, and for free, is on the public tours at Clos Pegase in Calistoga.
Sonoma County is full of first-rate brewpubs. You can find them in Petaluma, Santa Rosa, Sonoma, Healdsburg and Cloverdale. If you're in the Healdsburg area and you don't stop at the Bear Republic Brewery for a burger and a beer, well shame on you. Russian River Brewery in Santa Rosa is nationally famous with the beer crowd.
Yes, lots of great restaurants, but get a loaf of local French bread and cheese because it's some of the best in the world. There's a lot of olive oil produced locally, too.