To me its about style and durability, the 80's 90's seem to produce a lot of cars that were very bland and forgettable I am sure there were standouts in there and some cars have a particular fascination to an individual for what ever reason, be it that it was a family car from her childhood etc.
Its not an age thing to me that denotes a classic, indeed many of the current crop of cars I feel will become classics for there style detail though I have serious concerns for their durability due to the amount of electronics that now predominates all areas of car function, in 30 years time will you be able to get that ecu or door lock, body module, engine management ecu, I dont think so. The really disheartening thing about it all is that the last 10 years have seen some extremely nice cars being produced, there chances of resuscitation at a future date however is remote whereas cars before say 1980 only require mechanical maintenance and simple electronics / electrical.
Graeme