I'd donate. As long as I know my donation is going toward Lilypond
development, and that Lilypond users on the whole are happy with the
nature and style of development. (Reasonably regular updates to donors from the developer, with some opportunity for feedback on the main lilypond.org website, would do it for me.)
As the previous poster wrote about the other well-funded group, having a
board of directors etc. doesn't guarantee that donations will fund
development. It would not matter to me whether there were that kind of
formal structure or whether I was donating directly to the developer.