I find 4000 a big put-off. Are there that many scales in use worldwide?? If it were a few hundred one could at least make some headway.  My guess is that most of them are some kind of mathematical experiments.

The problem as I see it is like this:
Mathematically: The number of scales is worse than uncountably infinite (powerset of R). So for mathematical tractability one needs to work with genera, eg
- Equal tempered scales (not necessarily only 12 notes)
- Well tempered scales (all/notes usable, all subtly different aka Bach's WTC)
- Meantones
- Justs with various cut-off rules

And then criteria for 'badness' http://x31eq.com/badness.pdf for comparing these

Musician-ly: This is a pain. I just want better sound than ET. And a few rules of thumb to make sensible choices.

Personally I can say that after I got my keyboards with a handful of tunings a new world has opened to me.  If only I could have done some of that with timidity/fluidsynth...

Rusi
--