The classic car market has already decided what is classic, and what is not. That ship has sailed and we're* not on it.
If it's worth a lot of money (10 grand upwards) it's a classic. Mexico, 20000GXL, CX Prestige, XK150, 205GTI, 993C4 etc. Serious money.
If it's still worth nothing (Sxsxara, Peugeot 406 Rapist, an old Mondeo, E46 318Ci, Rover 75, Vectra, XJ40 then it's not. Light iron valued by weight.
Don't waste your time trying to work out what the next hot ticket is because there isn't one. Any value rise in some wanked 23 year old Jag will be used up keeping the fucking thing going.
* Well. Many moons ago I was given the rusty shell of a 1970 Escort Twin Cam. And since 2014 I've had the V5 for it. I have a window seat for the main event.