I agree with Hutcheon's depiction of postmodern parody as "value-problematizing" rather than "value-free". She states, "Postmodern parody is a king of contesting revision or rereading of the past that both confirms and subverts the power of the representations of history." (94) Indeed, stripping the meaning from past styles/conventions while maintaining some semblance of their structure will inevitably make some statement about our current relation to that past.
Although I agree with Hutcheon that postmodern parody is useful in contesting representations in history and the history of authorization, it seems to be a device that can easily slip into the (scaaaary) category of Jameson's pastiche. It's not just that it legitimizes that which is parodied while subverting it--I actually think that such double-codedness, that is must work within such contradictions and problematic relationships, makes it an especially complex and interesting form of art & representation.
(Note: this is much longer than I expected. I recommend reading the last two paragraphs and returning to the beginning if you're still interested)