Anything is worth what someone is willing to pay for it. Find the right buyer at the right time with a lot of cash and a need to have it, and something can sell for a premium. I'm 80% done with my restoration of a 615, and it's a gift for my Dad and would love to tell him it's worth $6500
But since it won't ever be for sale, it does not really matter.
I used to practically live at the Barret Jackson auction site the week it was on when I lived in Scottsdale a few years back. It's insane to see what things sell for sometimes. I remember a 57 Chevy with 56 original miles on it sell for over $250,000 (10 years back)! Good place to sell, but not always buy unless you have deep pockets and a "have-at-any-price" attitude. One year I bought two cheaper cars at the Kruse International auction the week before Barret, got them listed into Barret and netted a couple thousand more each than I paid the week before just for driving them across town - ahh, good times!