99.9% of people never thought when buying any car back then it was going to eventually be restored or coveted if still in nice shape 20 - 45 years later and did little to preserve them so not that many survived of anything except a good percentage of muscle cars, beloved family cars, guys like us getting them later not new and preserving or repairing them. Yes there are exceptions like TNTroopers car, or the grand dad that bought a car new drove it for a month or year, died and it sat in the garage but those are the .01%.
Cars like your station wagon or even high performance A, B, or E bodies for instance for the most part didn't survive in huge numbers/percentage due to many many factors.
Since the 80's people have had the idea of buying something sporty, muscle car'y, and keeping it nice and low miles to eventually make money on it or show it and be proud of being that guy with the foresight to keep it. This was brought on by the Muscle car price boom in the 80's and on ... but they don't realize the difference in circumstances. I recall in, I think 1978, magazine articles on the select buyers that were allowed to purchase a 25th anniversary corvette pace cars already had $$ in their eyes and were going to put them back and be rich in 20 years. A friend did this with a Trans Am in the 80s or 90's.
A. People didn't think to buy something and put it away in the 60's
B. There were far fewer of the truly rare, highly desirable hemi/6 BBL/440 HP convert cars then like Dave said than compared to the number of loaded new Challengers, Mustangs, Camaro's etc and the top end loaded cars before them back to the 80's - 90's.
C. Packages are used way more in the later era than in the late 60's / early 70's. You want an SRT and it's loaded automatically .. you wanted a 70 Hemi RR the car came with things to make it live and handle better on the street and to handle the extra weight .. transmission, springs, cooling, torque boxes .. no comfort, rallye/road wheels, tic toc tac, Air grabber hood, radio, trim options etc. Those things were all extra
D. There will probably be more of these metric challengers in 45 years (if there are still fossil fuel burning cars) than there are of your Station wagon today.
I doubt the metric challengers (they have built a lot) will be as unique in 45 years as your station wagon is today so yes, your car is rare today, unique that is survives was/is a cool color, and many people had something similar and appreciate it. I have had people come up to me at gas stations or anywhere else they saw it and comment on EVERY old Mopar I have ever driven, incl my Sport Fury and 300, my Dads Fury's, 66 Newport, 68 NY .. all of them .. since 1981 when I started driving Dads cars and I got my first RR and it was only 11 model years old then.
I am not putting your car down at all and I'm glad you have it and I'd love to check it out where ever I see it. I see several Metric challengers on my way to work (7 MI) and I see several every day on the road and in parking lots, dealer lots. I would not stop to look at one now at a car show. In 45 years maybe.