For starters: I’ve always done it.
Always? Yes, in fact, always. It’s a tradition that started when I was six months old and referenced Go, Dog. Go! during a Skype with Granny. I continued to do it with my Jigsaw Jones series, and carried it over to Justin Fisher Declares War and other books. Basically, I like giving the nod to real books that I’ve enjoyed. It’s also, hopefully, a way of linking to the reader, by mentioning a title that perhaps he or she has read. In the case of Kurt Vonnegut, it fit Corey’s character — he would like Kurt Vonnegut and, I think, that inclination would tell us something about Corey. You are what you read, and what you eat, and what you wear, etc. As I wrote of Corey in the book, p. 81: “He had the rule-hating gene in his double helix.”
And, absolutely, I do it for myself. I read Vonnegut in my teens — my generation’s YA — and still do. Still admire the man, the writer, the rebel mind. I don’t know how many teenagers read him nowadays, but I know I shoved Slaughterhouse-Five and Sirens of Titan into my oldest son’s hands.