Not all cars remain desirable the early series 1 Rx7 has always been a popular car and probably very difficult to find in original shape by now.
I certainly see a lot of 90s cars becoming cult classics. Silvias, Supras, Skylines, rx7s, wrx's, evos etc..
They are all very popular even now, no reason in 30 years they won't bring mega money to my mind. Especially in original shape as so many have been modified extensively.