Speaking as someone who's been playing classical and new music as an avid amateur (e.g. community orchestras, university orchestras) for several years, stuff like that isn't meant to be enjoyed as such. You don't put it on and relax with a glass of wine like if you were putting on a Grover Washington record or something by Sibelius.

I wouldn't even say it's supposed to be in the group of "challenging but at least somewhat structured and therefore listenable" not like In C (Terry Riley, if you're curious) or Music for Pieces of Wood (Steve Reich).

It might be intended to challenge what we think of as music, or challenge our assumptions about mechanization and culture. I'm not at all familiar with Conlon Nancarrow, but if he's in gallery exhibitions, and not on tour, that's the angle.