I once encountered a beautifully customized Hupmobile sedan at a World of Wheels type car show. The owner/builder was there and I asked him, why customize such a rare car? He said it was about cost and availability. I asked the same question to a fella with a '66 Mustang fastback who had replaced the entire drive-train and suspension with something modern. He said it was about drive-ability. They both wanted to enjoy their cars, to drive them.
And I agree with both. My favorite muscle car is the '66-67 Charger. If I was given one today and the $$ to build it, it would have a modern 6.1 hemi and modern suspension tomorrow. However, If someone gave me a low mileage hemi car, I could not in good conscience do the same thing to it. I would sell it in a heartbeat to buy something I could drive without the guilt.