I posted this comment on Matt Merrill's post about Dylan. Matt was responding to this piece (which I have not read yet).
First of all, it's a little hard to test Dylan's lyrics as poetry, since his best texts are ones that one is mostly already familiar with. Perhaps Andrew Motion (and you and I) should have read the lyrics to all the songs on "Modern Times" before listening to the CD. An experiment for his next album?
Secondly, I'm a little unsure about the idea of "depending for effects on the music"? It's hard to separate the music and the text, of course, but just because the music provides effects does not mean the text could not stand alone. To use your example of RT: "1952 Vincent Black Lightning" is a wondrous text. I can't imagine without the music, because I know RT's version too well, as well as Greg Brown's superb cover of it on his "The Live One," but the text is still flawless.
Finally, I have a collection of Greg Brown's live covers of Dylan that is fantastic. I can send you a copy if you like.