Most of what you say I have no issue with. Though this part I do take slight issue with. If we are saying it is based on numbers produced. Then this car has every chance of doing the same as the original stangs. If you do the math on the original 64.5-66 mustangs. There were over 1.2 million made (Rough math puts it at 1,287,000). Now while there was an additional bodystyle (Coupe,fastback,vert). There were far more made. Now mind you I am not saying this car is going to be worth a lot of money in 40 years. Though i do agree it will probably be worth more than what you have paid for it. Much like the originals are worth more than what people originally paid for them.
Well as I said, S197 Mustangs will hold their value far better than any old 4 door sedan or SUV. But as stanmckinney pointed out, other than a few rare models, nobody is going to get rich buying a new S197 today and hanging on to it for 20 years. I was around in the 1970s and back then 1960s Mustangs were a dime a dozen. You could pick them up for next to nothing. Yea I can kick myself today for not buying that GT-350, but at the time I already had 2 67 Mustangs so what in the world would I have done with a third? I didn't have a place to park another car so I would have to pay $$ to garage it.
How you will come out ahead with a S197 is the exact same way as people made out on the 1960s Mustangs. In 5 or 10 years few people will want S197s. That will be the time to pick one up cheap and wait another 15 years.