All you say is true. Lots of variables, lots of exceptions.
The winter may not be the best time to sell a collector car, but I've had some luck in January and February. It's a new year, the days are getting longer, car guys start thinking of spring and cars.
I suggest eBay and/or Hemmings Auction.
I sold several cars on eBay before BaT came into its own. I list as an auction without a BIN price (a BIN will scare off some buyers who would have ended up bidding the same number in an auction) with a reserve that is the lowest number I can live with...not the number I "want". I run for 7 days (10 is optional) thinking I will get more "auction fever" in a short auction than a longer one. Lots of pictures, linked or embedded video, a complete description, show and tell all the warts...it's the right thing to do and I felt it gave me more cred as a seller. The listing should be clean and complete but avoid looking like a dealer. It helps if you can write some HTML. The worst thing that can happen is that it bids short of the reserve but gives you another data point as to value. The best thing is that it at least makes reserve and maybe goes nuts over the reserve.
I have not used Hemmings, but I believe they are #2 in online auctions. Very similar to BaT. Again, worst case another data point. Best case it sells for your price.
I have also had luck getting the car for sale out and about at car shows. It's easier for a potential buyer to get excited being with the car and owner than on a computer monitor or smart phone. Someone who never thought they wanted an E9 can easily fall in love with yours in person. The bigger the show the better but most of those aren't for a while and may involve transport expense for you.
In any case, good luck with the sale!