Interesting thought I had this morning. Back in 1972, my stepfather had a
1956 Thunderbird, with the two tops, portholes, AT 283, Continental kit. It had about 70,000 miles on it, about 2/3 through it's life span. It needed an engine rebuild, a complete going over with a spray gun, tranny work, but had almost NO rust. It was an OK car; obviously the best part was the top-down cruising. Other than that, it was rode hard and put away wet! The paint was cracked and crazed, the chrome was pitted, the ragtop was rotted, the headliner was falling out of the HT, along with the back glass. So, you leave the tops off and cruise in nice weather. Everyone went Ga-Ga nonetheless. 16,450 were made for 1956. The car was 17 years old.
In my garage now I have an '88 Supra. The engine is good, the tranny has some issues but I have one available for $100. The paint is good, the interior is almost excellent; there is one rip in the driver's side bolster (surprise...). It has leather seating and the "Sport" (targa) roof. Rust is minimal. It has about 170,000 miles, or about 2/3 of it's life span. There were ~16,500 of them made. It's 17 years old.
So why was one considered a classic and the other simply a 'used car'? The Supra will certainly outhandle the T-Bird and is about equal in performance.