How do you get information on what older cars are sought after currently?
I like to browse Bring a Trailer. Very interesting to see how the auctions turn out.
You can use Hagerty to look up specific vehicles.
Bring a trailer tends to get a lot of exposure, and is generally thought of to be the height of the market. It also shows what's hot currently, and isn't necessarily a future predictor.
It's fantastic for daydreaming though :)
Really, to predict the future, you want to look at what was hot about 20-30 years ago. The idea is that you take the generation that's in the meat of their earning years, and look at what was popular or desirable when they were in high school, because that's what they'll buy to try and recapture their youth or acquire what they couldn't have then. That's why about 10 years ago muscle cars were all the rage, and now 80s sports cars are blowing up (air cooled 911s, Ferrari 308/328). The thinking is that the next big thing will be 90s Japanese cars, and that's what we're already seeing, such as the NSX, FD RX-7, Supra (they never really went down), Integra Type-R, etc. You also want to consider what cars/features aren't available on the new market; manual transmissions are on the wane, electric steering is taking over for hydraulic (generally considered a backwards step), etc. And you have to consider if the old car is superior to the new one; for instance, no one is going to pay huge money for an old Miata when a new one is available off the showroom floor for reasonable coin. But if you find something that was desirable and discontinued without a good replacement (like my S2000), that will have a little more runway to appreciate.