Of all the poll results, I was most interested by the fact that 64% of respondents wanted more level 20-60 content and only 15% wanted more end-game content. Also of note is that only 12% wanted more races in the game. So in other words, people don't want new "starter areas", they want alternatives to the "grinding content" that they've run so many times they can do it in their sleep.
I pretty much agree with all the poll results and wonder why Blizzard seems to have turned a blind eye to the obvious. I think it's fair to say that most of us have one or two high or maxed-level characters, and a handful of lower level characters we "mess around with" trying to find something we like. So why don't they develop new mid-range content?
What format do you see new mid-level content content being packaged in? New zones? New quests? New instances? What about just new items? Personally, when I played The Sims, I always loved the "item packs" that gave me new items to play with in-game. They weren't a content expansion, they were pretty inexpensive, but they offered some new items to spice up gameplay. I think this could be a cheap way for Blizzard to throw the mid-level people a proverbial bone without spending a lot of development time.