- Ives (admittedly his more traditionally tonal works), in particular his Second Symphony
If there's a “lesson” in this, it's not that people will like new music if you cram it down their throats enough (though I think this is the first time my mom's been drawn to a piece for an essentially intellectual satisfaction). My guess is that she liked the music because it met her on territory she was comfortable in. Though she hasn't touched the instrument in a while, my mom took piano lessons throughout the early part of her life. Though Rzewski's style of virtuosity was certainly new to her, she was able to relate it her knowledge of the instrument. Instead of being repelled by his style, it intrigued her.
I guess this situation speaks more to developing musical literacy than a taste for the new. Whenever non-musical friends ask me to “teach them about music,” I just tell them to listen to a lot of music (with carefully curated suggestions of course ;)). It's possible to appreciate music just out of the pleasure certain sounds bring, but a deeper appreciation comes from picking up on the practices that have persisted throughout its history. Like with any other language, the only way to gain fluency is through immersion.
My mom's knowledge of idiomatic piano writing spelled the difference, so far as I can tell, between her liking the piece and it being another instance of me playing unseemly “sounds” for her. I don't have any high expectations about further emendations to the list above, but it's nice to see that it wasn't as closed a book as I thought it was.