The key here is "excellent condition" or better than they came off the assembly line.
While it would be nice to figure that the pile of rotted junk behind the garage is worth several thousand dollars because it is a Kaiser, Frazer or Henry J and hope that fully restored it would sell for $20-30,000 dollars, the reality is something else. Given the current cost of restoration labor and re-chroming the parts that are no longer easy to find as NOS, restoration would be a labor of love unless you can do all the work yourself. As for fully restored, unless the car has an interesting history (like the 1948 Manhattan owned by movie and radio stars Phil Harris and Alyce Faye) or you find just the right buyer who doesn't care about how much is spent (and there is not much of that going around these days) the majority of even very good restorations (except for Virginians, Dragons convertibles and Darrins) will be hard pressed to cross the 15,000 plateau.
Check out the NOT SOLD efforts at automobile auctions and look at the numbers yourself.