Sometimes it's just luck. I sold an RX-7 like a year before *that* movie showed up and they all got snapped up and destroyed by clowns. Could have easily 5x my money off of that one. Generally though, you make money trading cars, not hoarding them.
I think it's better to buy something to enjoy rather than expect to make money off. Buy near the bottom of the depreciation curve you get some fun out of it and you won't lose too much to depreciation. I still need to own a V12 car at some point and have been eyeing Ferrari 456's and DB9's for a while. Prices on them have been mostly flat for a few years now. There's definitely a market split between cars that just sit around in storage and for cars that people actually drive. You see cars with like 12k on them and also cars with 100k+.