This sentiment is almost exactly what Douglas Hofstadter and, indirectly, Tom Lehrer express in the book Le Ton Beau de Marot.

"In other words, Lehrer said, he had simply found himself dreaming up odd images that never would have occurred to him had he not been bound to make one line rhyme with another."

And you should see Things That Rhyme With Orange as an example of such creativity.

And Hofstadter talks of poetry translation, surely a task with some of the most demanding constraints, requiring preserving meaning certainly, and one would hope, the rythym, rhyme, and feeling of the original work. The main thesis here seems to be "Try Harder", (a good motto to remember when creating E2 nodes, and one I should certainly try to remember), and several truly amazing examples are given. The idea that constraints (or boundaries) can have a positive influence on creativity is demonstrated in spades in this book.