I think the rhyming version of that poem of mine is better mainly because it fills out the idea so you get a fuller picture of the extended metaphor. (I wrote the thing on the spot in a half hour, though, so it's just meant to contrast with Gorman's fake poems.)
I also like the way rhymes can add a hint of charm, assuming the rhymes don't become intrusive. But it's harder to be creative and precise when you're rhyming, because of the added constraint. You can tell right away when reading a poem, whether rhyming got the better of the poet so that he or she focused more on completing the rhymes than on saying what she really wanted to say or on being semantically creative.
I think the lyrics in operas are more about story-telling than about poetry. The more poetic and creative the lyrics, the more the musical accompaniment will be a distraction and make for a jumble.