I asked my friend Arthur what he thought of Kristen Hoggatt’s essay, and this is what he wrote back:

Music affects us on a more primal level than language (a fact Schopenhauer made much philosophical use of) and it will tend to overshadow (distort, transfigure) whatever words or lyrics you set to it. A song can survive, even “ennoble” mediocre lyrics; but no lyrics, however brilliant, can survive unmemorable music. It’s great when words in songs are intellectually or aesthetically stimulating in themselves, but the qualities that make the words seem to work as poetry when set to music are not necessarily the qualities that would make them work as poems. Who worries whether the librettos of great operas are poetry in themselves? They usually are not, and composers like Richard Strauss, aware of the greater authority of their art viz a viz merely literary merit, have been brutal with the literary pretensions of their librettists (like poor Hoffmansthal, Strauss’s collaborator on many of the great operas): give me what works (serves the technical needs and imaginative ambitions of the composer, me), not what seems beautiful or profound to you as a poet.
The poets of our tradition stopped being troubadours centuries ago. Poetry is its own music, both for the ear and for the imagination. It comes into its glory read aloud, but not necessarily when set to music. (Which is not to say that great poems can’t be set to great music. But it’s surprisingly rare. Schubert was inspired to new heights by Heine, but he could compose equally great songs to fairly fun-of-the-mill poetry.)
Music is a Dionysian art; poetry is Apollonian.
P.S. I forgot to add something about Stevens, a propos of Simon’s comments. Strauss often cut out metaphors and verbal associations he thought crowded the aural canvas and distracted from the music. A poet like Stevens wants to pursue verbal associations and imaginative ideas wherever they take him, to let poetry revel in its own extravagance, its own “fictive music.” Poetry is the music of the mind in motion among its metaphors, and it addresses something solitary and inward in us–just as music itself often does, when it isn’t telling us to get up and boogie.
Which echoes Shanna’s observation that good music can make up for insipid lyrics every time. Sometimes trite sentiments or outright surreal nonsense can still be fun to sing if the rhythm and melody are too irresistible.