Why is poetry important (or not)?

It is probable that the value of poetry lies in the fact that it IS of little economic value.  There is absolutely no ulterior motive for the poet to write except one of altruism (or the almighty ego).  A poet can't really be accused of "selling out" (except to Hallmark, and the term "poet" really need not be applied in that domain) because really, you'd have to be flat out stupid to think there's any real remuneration involved. 

Being a professional poet is a little like running an op shop.  It's much more about love than money.  Additionally, you have to weigh what's "cool" against what people are prepared to accept.  (And you tend to deal with a lot of smelly people who smoke too much dope).

In the long run, for a poet to be relevant he/she must have a finger on the pulse (hooray for cliches) and cannot be taken in by glossy propaganda.  This is why "freedom of the press" is supposed to exist -- that fourth estate that should bind and check all the others.  Sadly, rather than being a guardian it has become both hangman and hanged, a tool of whomever will take it up -- because of commerce. 
I think that's probably a bit off the track... oh well... blame postmodernism and its refusal to adhere to straight lines.