I think the real decider on how classic cars are viewed will depend largely on what happens with oil production.
If it remains steady, i would expect to still see historic racing groups in regular (4-5 times a year?) outings, people will still collect them and show them at events, ect.
i would see the icon cars of the 70's being around still, although in very limited numbers, and almost all in origional appearance.
90's cars seem a bit hard to pick, i think it'll be the same deal, the icon cars will be prevalent, with quite a few modified examples.
Anything from about now-2020 onwards will be a predominant vehicle of choice for mods, racing, individualisation ect ect, like what we see now with the current range of 30 year and younger cars.
If oil production becomes reduced, and the world finally turns towards a green power supply, i think that will spell the end of the car scene as we know it, but on the other side, cement it into a history that wont be forgotten for a loooooooong time.
If fuel were to cost $15 a litre (figure out my bunghole) the few passionate people will still collect and show thier cars, but it'll be a less common occasion when it happens, as such, there will be a better turn out, a bigger wow factor ect.
Im sure some collectors will still drive occasionally, and maybe there will still be a 'historic style' lap of a track.
I have no doubts that no matter the state of oil production, there will allways be vehicle racing, man allways wants to compete and go fast, its instinct. It'll just use the power source of the day. (off topic, mandate that F1 has to be powered by Electric or Hydrogen fuel cell and watch the tech become massively advanced)
The cars of our time will simply become part of that scene, similar to when you go to a car show these days and see 70-80-90yr old blokes with thier 1900-1950's pride of joy sitting, looking like it just rolled of the assembly line.
If you get the chance, you should ask some of them the same question, to get their perspective as people who have actually lived that longer period, watching everything change.
no matter what happens though, my concern is that valuable skills and knowledge is being lost as time progresses.
The repair industry has become a 'replacement' industry, its uncommon to find a younger person who has the skills of his predecesor in seamless panel repairs, or even fabrication from scratch.
In another 30 years, will that person with those skills be 1 in 1000? 1 in 10,000? more?
I remember having a discussion with an old fella, he owned a vintage range rover from the 30's (there abouts) and was in the process of a long restoration on a Model T ford.
He was saying he would donate his cars to a museum when he passed on, as he didnt know anyone (including his kids) who knew how to maintain vehicles from back then.
Me being a bit roostery said it couldnt be that hard, any mechanicly minded person should be able to do it.
Do you know how to De-coke an engine? i dont, as he pointed out to me and that was a regular maintenance item of the era.
It seems that alot of the knowledge we have may be lost over the years unless we find and encourage people to carry on our passion.