almost every car will eventually appreciate in value, it's just a matter of time and availability.
C4's are starting to tick upwards. Not very quickly, but they are starting to climb.
Successive generations will likely do the same. I would suggest the C8 will appreciate faster and sooner than most, simply because it is such radical departure from all Vette's that came before it.
One need only look to the C3 for a potential worth path most vette's will follow. The C3 came out oh so long ago and sold like gangbusters. It also had a super long production run and a "gagillion" of them were pumped out. Shortly after the C4 came out, you couldn't give a rubber bumper Vette away. Popular or not, they just didn't command a high price point. A lot of that had to do with the smog era engines they had in them as much as the rubber bumper look.
But then a funny thing happened; the prices starting ticking up years after the C3 went out of production. These days, the rubber bumper cars are still not mega-collectable high dollar cars, but you can't buy them cheap anymore. You're looking at somewhere in the 15-30G range to get a nice one. People who grew up in that era and couldn't afford one are now searching for the car they couldn't buy when they were young. Now they've got money and and they're willing to "belly up" to get the car they wanted and couldn't afford. It like a "bucket list" sort of thing.
The C4 is "sort of" following that path. They cranked out a bazillion of them, there were some ultra high performance models and shortly after they weent out of production, you almost couldn't give them away. Now, the prices are starting to rise. Just like the C3. A regular "run of the mill" C3 or C4 is never going to command the top dollar, but they are climbing.
Now the C5/6/7 generations may have a little harder time following that pattern. It has nothing to do with the cars, they're fine examples or RWD ultra performance cars. the problem I see that C5/6/7 cars will have to overcome (to become collectable or valuable, which are not necessarily the same thing) is that the generations that grew up with them are far less interested in cars and far more interested in tech like computers, iphones, etc. Cars to recent generations are not a hobby or lifestyle, they're appliances. There are some out there who are still gearheads, but no where near as many as when I was growing up. When they get "nostalgic", they go looking for an "Apple II", an "NES" console or a "Simon". I'm guessing this will keep the prices relatively low and may also drive down the prices on the 60's collector cars as well. In fact, there's already a noticeable "softening" in the price of the 60's collector cars. They're still stupid overpriced in my opinion, but the dollar they command is weakening every year.
But, as far as what car to buy now?
Whatever strikes your fancy.
Buy it, drive it, enjoy it and then do whatever with it. Collect-ability or resale? Meh, give that a pass. These cars are meant to be driven and enjoyed. Can't do that sitting in a garage, afraid to scratch the damned thing. not only that, for aC5/6/7 to get some "collectability" it's going to take decades. LIkely longer than you will live. So just buy what you like and can afford and go wear out some rubber every chance you get.