Deaf Eddie, i agree with what you wrote, up to a point. However, there are some very big exceptions that i can easily point out.
1985-1987 Buick Grand National
1989 Trans Am GTA Turbo
1990-1995 Corvette ZR1
1980-1984 Renault R5 turbo
1976-1981 VW Scirocco
1983-1984 Hurst Olds
1990-1994 Nissan 240SX
There are a lot of others that see escalating prices much sooner than 30 years. Time will tell the tale i suppose...