There has been a lot of stupid money driving the collector car market, particularly in muscle cars. The Challenger and 'cuda were marketplace flops in the early 70s and generally considered a poorly built, poorly running POS, but for some reason, they were commanding six and seven figures at Barrett-Jackson (which is the last place I'd ever buy a classic car).
I really like the 61-64, 71-72 and 77-79 DeVille, and there are definitely some good buys to be made on older Cadillacs. Collectable? Probably not. Classic? I'd say so. There's something to be said for owning, driving and enjoying an old car.