Your logic is flawed. Collectors are a niche demographic. Popular vehicles desired by the masses are typically NEVER collector cars. Vehicles like Mustang GTs, SS Camaros, Subaru WRX, and so on are mainstream vehicles that will have next to no collector value. This is because there are hundreds of thousands of these cars available and everybody wants one and everybody has one to sell. Thus, market competition ensues and the prices on them stay relatively low. I point directly at the "collectible" 65-70 Mustang market. The run-of-the-mill 289, 302 and 351 coupes are a dime a dozen. You can get decent condition ones for under 20 grand. Fastbacks are collectible and fetch a premium. 390, 428, 429 equipped models fetch more again. Then, you have the special edition Mustangs like the Boss and Shelbys (I don't count the Mach 1 as it was a mass produced trim line akin to the modern California Special Edition... see: not rare). Those fetch a massive premium amidst the sea that is the bazillion other Mustangs on the market.
Now, collectors are a small niche market buyer. Most of them employ brokers to locate or find the cars they want at auctions. They are after things that very few, if anyone else has. Rare cars, powerful cars, limited production cars, etc. By default, they don't want a 66 Mustang 289 coupe painted Wimbledon White. In addition, these collectors are -not- the types who don't give a rip about cars. There's plenty of those types, they're called Tesla buyers.
Back in the late 70s and on into the 90s, car culture slipped due to the fact that almost every car made during the dark ages of car manufacturing were poor quality and utterly forgettable. Very few domestic cars made during this time period will wind up as collector items. During that period, people were also less inclined to be gung-ho for cars as they were all homologated to being fuel efficient, low power, low thrill rides. Even the Fox Mustangs and Camaros of the day were under 300hp until the early to mid 90s. They were all just boring, bleh pieces of form molded plastic trimmed junk with bad electronics and the collector market responded thusly. There were still collectors during this period, but they ran more towards things like Porsche and back towards the pre '72 muscle and sports car classics. It was also during this period where you first saw a big run on the '65 Toyota 2000GT (which trades for up over $1 million USD today). The average Joe who loves his 2002 Mustang GT likely has no inkling as to what a '65 2000GT is.
Now, let's look at Challengers/Chargers. Like the Mustangs and Camaros, MOST of them aren't going to be worth big money, pretty much never. The Hellcats are a different issue. Again, these have to be separated to determine their collectability. Base model Houndstooth cloth Hellcats with no options will be worth nothing. Dodge made a lot of these, especially during the '15-'17 model years and many, if not most, wound up as lease vehicles. In general, leased cars are not maintained as well and will have numerous owners during their lives. A car with 5 owners that's 10 years old is something no collector wants. So nix those.
Collectors interested in the Hellcat market are going to look for a few specific things: First - Unmodified. Bone stock. Unmolested. Any Hellcat not in this category will not be collectible. Second - Production year. 2015s and 2023s will be desirable as they're the first/last. The 2015 started it all and the 2023 will be the final evolution with the most improvements. Third - Rarity. Demons go first here. Then, the other rare Hellcats and Redeyes will stack up underneath. Redeyes will always carry a premium over a Hellcat. The rarity of the car will determine interest level. Car guys like a car with a story. Thus, the Jailbreaks will be unique in this group in that they should all be pretty much unique and exclusive unto itself. Further, like the Boss Mustangs, the Jailbreaks will be limited AND be the most powerful non-Demons made. They'll fetch a premium.
The SS will be desirable as it's a relatively low volume max strip performance sub model of the Redeye. Further on the SS, most are likely going to get tracked, if not regularly and many will get modified. Thus, unmolested Super Stocks will become exceedingly rare. Collectors will pay a premium for a low mileage, unmodified Super Stock. Billy Ray down the street will be interested in a ported and cammed SS, but Billy Ray doesn't have $100,000 in disposable cash lying around. Thus, the modified SS's will end up similar to the leased Hellcats in that collectors won't want them and the value will tank as the people who do want them and have the time to chase down mod issues have more limited funds.
For a Hellcat to be collectible, it has to be unmodified, rare, and its production year will amplify the value. There will always be buyers for these cars. 10, 50, 100 years in the future. Kids today might indeed be the buyers of the future, but not all kids are car dumb. There's an awful lot of young people at the racetracks I frequent. Like I did at their age, sometimes they're driving rip-roaring pieces of rolling crap, but they're involved.
In 20 years, if a car person of any caliber hears the word, "Hellcat," trust me, they'll know what it means. 16-22yr olds today who can't afford a Hellcat now will be the big spenders of tomorrow. I fell in love with the Torino when I was a little kid (no idea why). My 2nd car became a 70 Torino 429 Super Cobra Jet. Many of the Hellcats sold in the distant future are going to go to people like me who saw a Hellcat when they were 8 and will be in the position to snag one off the auction block. It doesn't matter so much if an M5 is faster, or a C8 can corner better. The Hellcat has a lasting mystique about it that has been prevelant since day 1. That charm will only increase after they're gone. Trust me.