Thanks for the Gaiman quote. From what I've heard, you can definitely get away with a lower wordcount in YA, and I'm guessing Coraline and Stardust were sort of counted that way even though they have appeal to adult readerships. Of course the name recognition changes everything, but it's revealing that most of his work is more around the 100K mark.
Quick update on the original post: my WIP is quite mysterious in tone, starting out, and I thought I was maintaining that tone by not including much background throughout the novel. However, I had an epiphany a couple days ago that it may just end up bewildering readers. A mysterious beginning is great, but I think I need to flesh out the history as I go along, giving more and more context to help the reader understand this world. I identified some ways I can do that without being annoying, so I should end up with a substantially higher wordcount when I'm done.
Thanks for all the comments, it really helped!