Why do people love dichotomies? You'd think we're all programmed like software, yes/no, black/white switches clicking in our brains, cataloguing every impression and experience good/bad, hell/heaven ... Wait a minute -- we are!
So any discussion of accessibility and difficulty in poetry, in any kind of writing, must invariably be preceded by the word "versus," as though it weren't a continuum, a spectrum of colors. Most painters I know appreciate a big palette and a broad spectrum from which to choose when working. Most academics love the word "versus" or even better "in contradistinction to" (how inaccessible is that?).
I could rest my case right there by implying that all creative activity considers the spectrum view of life, while all analytical activity views the versus. (And those of us with alliterative disorder can't resist speaking merely for the pleasure of its sound.) I could stop here, and let you come to your own conclusion, but what's the fun in that? Let's jump into what some are discussing on this topic, hopefully without indulging much in the Poet-Laureate-bashing urge that seems to afflict many poets at this season. Though I defy any of you to find a discussion of accessibility that doesn't have his name in it, as a year or so ago, any such discussion inevitably mentioned Billy Collins. (And what's so accessible about Zen humor?)
Here's Emily Lloyd with a fascinating argument, not for greater accessibility in poetry, but more visibility. Michael Whalen has a beautiful essay on the topic, addressing mostly accessibility of subject, on Slant, Issue 6. He makes a good case for the subtle dimensions in the spectrum of accessibility that are unique to poetry, as apart from other kinds of writing. He points out poetry's layers of meaning in his comment that what is foregrounded and what is obscured has a meaning of its own. We read poetry not only for what it says and means, but for how it does so.
I venture my own modest generalization here. We read poetry because it is more difficult, and layered, than other forms of writing. We prize its obscurities, as long as we can barely keep up with them. We value the how as a continuum of the what.