I wonder what effect all of the technology in current cars will have on their "collectibility". It doesn't take much in the way of sophisticated equipment to keep a 69 Z28 or Boss 302 on the road. The same can't be said of anything currently pounding the pavement.
Diagnostic equipment comes and goes, as do the various CPUs currently in vehicles. Can you imagine the issues in trying to find specific circuit boards in 20 years time? Popular cars like the Mustang probably have a fighting chance simply due to their popularity. Rare cars now will require a great deal of time, effort and skill, not to mention deep pockets, to keep rolling.
Part of the reason the original muscle cars remain so popular, is because the cars that followed them were such utter crap. Anyone around that had to trade in their thundering Buick GSX for a FWD Skylark (or Fairmont, or Volare or first gen Accord or Crown) really had a sense of loss, and that the "good times" were over. If the next generation cars are significantly slower for fuel economy or ecological reasons, the current variety of performance cars could very well be as collectible as the GSX or Boss of the late 1960s.