Meh, how good a song is, how good the lyrics aren't always the same thing - and even really good lyrics, and really good poetry make it into song form occasionally - this famous poem, http://my.iciba.com/blog-3284714-198759.html , ultimately becomes this famous pop song - http://www.youtube.com/watch?v=Qz8-FzYxP3w - the rules between poetry and music are so mixed up. The song is nothing like the poem in context - the singer bends the words - first by making the speaker a woman, which changes much of the meaning, and secondly by emphasizing - the 900 year gap between the respective artist's ages also changes how the setting of the poem communicates.
Even something like Thomas Wyatt's verses written in Octaves were originally set to music (I found that out by asking a professor why the scansion on them was so wacky) - how does that effect the metrics of the poetry then, now that we no longer have the music? Are they better for it now, or worse?
Ultimately, I don't see a connection between good lyrics and good music - it's just that sometimes they go hand in hand, by some fluke.

