How long was your trip last year? If it was 2 weeks, have you considered that 4 cities in 2 weeks is very different from 9 cities in 2 weeks? I admit that the driving isn't as bad as I thought it would be--ViaMichelin estimates a total of about 32 hours (without any stops, of course). But all that moving around...
I've been to all your Spanish destinations except Valencia, and there's not one where I'd want to have just half a day (which is what you'd get in most cases with a one-night hotel stay). It looks to me like you are trying to squeeze 3 weeks of sights (at least) into a 2-week trip.
Barcelona is a large city with an extremely large number of attractions. I spent 10 days there last month and left things undone, just to give you an idea. I can't imagine having less than two full days there (not counting a jet-lagged arrival day), so it needs a minimum of the last 3 nights of your trip, and Enric will be along at some point to tell you that is criminally short.
I don't know Valencia at all; I'd say read about the museums there (which I think are a big part of the draw) and figure out how much time you'll want.
Of the remaining cities my favorite (I liked them all a lot) was Toledo. In addition to having a large historic district to cover, Toledo has many sights I wanted to enter, so I spent several days there. Some tourists make a day-trip from Madrid, probably just visiting the Cathedral and the museum and walking around for a few hours. Which kind of traveler are you?
I don't know how to distinguish among Segovia, Salamanca and Zaragoza in terms of time required. I guess if pressed I'd say a bit less time in Zaragoza and a bit more in Segovia. I preferred the architecture in Segovia to that in Salamanca for sure, but we're talking personal preference here, and there's a lot of ground to cover in Salamanca's historic district.
As for Bilbao and San Sebastian, both cities have attractive historic districts. At least in summer, SS's is much livelier/more touristy. Tons of tapas bars, etc.; it's definitely the place to be if you like that sort of thing. Bilbao's historic district may be larger, and it was far from dead, just not swarming with tourists. Both cities have very nice early-20th century architecture and are pleasant for wandering around. SS has the San Telmo Museum; Bilbao has the Guggenheim and the Bellas Artes. San Sebastian has a gorgeous beach, but I'm not sure you'd even want to walk along it in November, when I'm guessing it would be gusty and cold. I think you might pick one of those two cities, since your time is so short. Alternatively, you could stay put in one of the and day-trip to the other without changing hotels.
I'd suggest checking the historical weather patterns for your planned destinations. I see that San Sebastian gets an average of over 7" of rain in November (Bilbao's at 5.8"), which sounds like a lot. SS gets an average of 96 hours of sunshine for the entire month (Bilbao's at just 88).
I'm not sure your other cities will be much warmer than the Basque Country, but they may be drier (I haven't checked). If so, I'd be inclined to focus my November time away from the northern coast. But, as I've said several times before, weather matters a lot to me. A lot of people are far more tolerant, and it helps that you plan to drive.