I would never trade my 72, especially for an earlier mustang. They are not that much different or heavier. They look every bit as good or better in my opinion. I love cars in general, but trade my car is something I could not do. The regular average person doesn't know the difference anyway. I cant tell you how many people have asked me at gas stations if my car was a 69. I have never gotten a bad comment from anyone about my car, and its not even that nice looking. Hemi Mopar? Awesome cars sure, but so is my Mustang. Forget about the potential "worth" of the car, that's not what these cars are about to me.
It really irks me when I hear people talk about how "big" these cars are. They aren't any heavier than most of the muscle cars of the era, chevelle, charger, etc. The Boss 351 was the fastest production mustang ever built for a long time.