We had an overall lovely stay at the Sonoma Hotel. You can't do any better than this location for access to things around Sonoma Square. Free parking is plentiful nearby. The place has a very historic charm to it (keys! Actual keys to your room!). And while the rooms are small, you have everything you need.
As others have mentioned, the noise is an issue. I'm not sure I would stay on the second floor again, given the opportunity for noise below you and above you. Every step the person above you takes is bothersome because, as others have said, the floors are old and creaky and it's not subtle noise. The doors are very thin, and each floor has a small common area where housekeeping does its thing and where people come and go, all of which can be heard quite clearly. We stayed in Room 27, overlooking the corner of 1st & Spain. That room is also next to the only set of stairs where people access their rooms. We had no issue at all with road noise, but there was a lot of noise from hotel guests. Perhaps the other rooms had better luck, but I doubt it, given that the others would be over the restaurant, which I imagine to be noisy in its own ways. Earplugs and white noise apps were a necessity for sleep here.
In short: I WOULD stay here again, but not on the second floor, and maybe not in the rooms that are adjacent to the staircase, given the tools we have to manage the issues of general noise.