I think it depends on whether you want contrast vs Single Thread, or complementary.
Spinster Sisters is a very well-executed, sophisticated-but-casual neighborhood bistro, in the true sense of the word. It is creative CA/global cuisine, very veggie forward and light in feel compared to, say, Valette/Healdsburg.
Valette is very good as well but the food and focus are more tavern-like, the food heartier and heavier although still well-crafted.
We found service at Spinster much better than Valette. YMMV.
Bird & Bottle would be most comparable to Valette: heartier food, generous portions. It’s good, but Valette is a half-level higher. Service at all Stark Grp restaurants (B&B is their newest) is a strong point.
Not familiar with Flower + Bone. Would not recommend John Ash: beautiful restaurant, mediocre overrated food. We were really shocked at how bad the food was. By far one of the worst restaurants we’ve been to in Sonoma Cty.
We really loved Bistro 29 when we first discovered it, and had two really excellent dinners. But the last two have been increasingly disappointing. Only the roast chicken was good, out of four entrees at our last meal there. It’s off our rotation list, but maybe jackiecat has been there more recently (our last meal there was May 2015) so things might have changed.