In an essay on the art of writing poetry called "The Dyer's Hand" W H Auden wrote some fairly positive things about the value of parody. As far as I can recall, he said that writing parodies was a valuable learning exercise for beginners, and also was the most effective way to criticise other people's poetry.

A form I particularly enjoy is the "variations on a theme" exercise - a sequence of parodies of a single work in the styles of different authors. A famous example which appears in several anthologies is "Old King Cole" in the style of half a dozen different poets, ranging from Lord Tennyson to Walt Whitman. Worth checking out.

Wassail!