great small boutique napa and sonoma wineries
Look to the wineries on the mountains: Spring Mountain, Mayacamas Mountain, Atlas Peak, and Howell Mountain all boast amazing, boutique wineries.
I would name some specifics, but they tend to get deleted because I used to work at some... But trust, mountain juice is stunning and the wineries are incomparable. They also get considerably less traffic and more personal tasting/service.
In Napa, heading up Spring Mountain is good as there are many choices, e.g., Pride, Cain. On the other side of the valley, consider Viader on Howell Mountain, and to the south, just outside the town of Napa, consider Hendry.
In Sonoma, consider Walter Hansel, WesMar, Littorai, mostly in the Green Valley or Russian River Valley. In Forestville, you could try Arnot-Roberts and Wind Gap (Pax Mahle's new winery).
Almost all of these are by appointment only, but appointments were not difficult to get and did not require you to be a member of the wine club. Some have a fee, others none.