@pastanaga - I can see your point, but I like to think of every aspect of the poem as contributing to it. If you look at certain poetry of Wordsworth, to carry on the example, he is actually quite cutting and cynical at the bottom of what he says. Would this be as effective if his poems weren't offering the contrast of such lovely lyricism?
Likewise, perhaps you're trying to get a meaning across that's fairly straightforward and brutal. If you tried to dress up the poem with rhyming and so forth, it wouldn't work.
Personally, I think that any meaning can be conveyed in a fixed verse poem, without compromise, as long as the fixed verse is allowed to convey its own meaning (and as long as the poet is very patient, as you're right, it can be extremely fiddly).