are 1970 and down 727s worth rebuilding

Absolutely it’s worth it. If you had both to pick from sure go for the 71-up but with the 70-earlier it’s easy to upgrade the few known areas that you’ve likely read or heard about. I run a 67 727 short tail shaft (bolt-on yoke) behind a 410 stroker, no idea the exact horsepower or torque but it runs consistent times, bests of 11.44@114 (likely would be faster in an A-body, I run an old van) dead hooking wheels just up with a Turbo Action 3500 tight.
Rebuilt the trans myself with a 5 red frictions conversion (5 thins in a 4 disc drum, originally was a 3 disc hub) upgraded bands, TransGo 3 shift kit some other things I can’t recall atm. I had it apart to inspect while doing the drum and friction upgrade and everything looked fine. Everything. I’ve done lots of runs as well as being street driven. No concerns whatsoever. Trans is original to my A100 van, that originally had a slant 6. It’s been around the block a few times.

I’d contact A&A if you don’t already know. They will hook you up with what you need to upgrade: Home - A&A Transmissions