On Nook and A5 prints, start a new page with each tune and centre vertically.. A5 mostly did, but ran into trouble with longer comments on a tune. This may give blank space after tunes where a long comment overflows onto another page, but I think for now it's better to have each tune at the top of the page. Or rather, and this is the other change, in the middle of the page. Centre the page content for A5 and Nook.

\documentclass[a5paper,landscape,11pt,oneside,openany]{book}