Every car ever produced, from any era, will at some stage become a 'classic', depending on your point of view. If it becomes a classic in the sense of the word that it will be 'worth a fortune' it's a completely different thing altogether.
Pick any car from 10, 20, 30, 40 years ago, and see what the values are now. Chances are they will be worth far less than when they were new, or at a guess, the same value depending on price index.
Take a 50's Austin A35, probably a few hundred quid when new, probably worth 3 or 4k in concours condition now. Or a Lancia Delta integrale. How much were they in 1990/4, 25k or 30k, not far off that now. Or a 1999 Merc CL500, how much is one worth now in comparison to when it was new.
However certain cars, which when 'new' were already classics, are the ones that usually increase in value.
There will always be exceptions of course, but very few.