[tubut]

Real value depends on condition, which seems to be closely related to the cost/time since restoration.

I don't trust buyer's guides (because the best, original cars change hands "above market value" without ever being recorded) or auction results (because the auction may involve "shill bidders").

About the only thing you can trust that should matter to you and your insurance is: "how much does it cost to buy or bring a car to the condition your car is in." So, the deeper question is "what condition is your car in" and "what cars in comparable conditions have been sold recently." As you probably can imagine, the differentiatior is documentation -- meaning lots of high resolution detail photographs.