"many songs recited or read give the impression of 'doggerel' - it's not until you put them in your mouth as a singer that they spring to life"

Actually that was exactly the point I was trying to make! Considered purely in terms of the written word, there is no real gap in standard or skill between a song like Maid of Australia and a typical broadside verse, and therefore I can't see any reasonable objection to the idea that a broadside poet couldn't have written those words, or the original from which they have evolved.

The point is, as Howard says, that the real, worthwhile creativity isn't in the original composition of the words. It's in the process by which they get turned into a great song.