I ran super tweets with my 57s back in the day-- Deccas, which I still have and Sequerras, which were a good substitute (also used ribbons).
It gave the Quad a broader sweet spot, given how beamy the original tweeter panel is- but it wasn’t a substitute for the stock tweeter. It was fun putting it together even with the subs available at the time (this was before subwoofers were as common as they are today- which I attribute to the home theatre boom of the ’90s). Sort of a mini-HQD system.
These days, I just run my Quads without add-ons, no aftermarket stands, etc. They serve well in a small parlor as part of a vintage system.
If I wanted to get serious about Quads as a main speaker-- I still know a few people who run them as such-- I would definitely look at a stacked/double pair.
Quads are sort of a perennial favorite- I’ve known people who got rid of them, only to buy another pair. As long as they are in good condition, and have been gone over (E Solutions added a protection circuit and more conventional connectors), you can enjoy them without worry. Classic speaker, despite its obvious limitations.
PS: I also had Crosby modded '63s, and though a better all-arounder, it did not have the magic of the '57 in the mids in my estimation.