I have the feeling that the focus of your efforts is going to change from goblins to whatever / whomever was responsible for the events three years ago... and (hopefully) that will turn out to be something suitably epic.

As for the "mid-core" argument, making NM harder could have accomplished that for a little while. The only key requirement for NM Alex is that casual players are able to clear it and see the story -eventually-. It wouldn't have been too hard to tune it such that it was actually a pretty reasonable challenge at i180, but pretty easy to clear at i205+echo as 3.2 came around. That way as people clear it (better players earlier, decent players after a few weeks, lesser or slower players down the road) they'd have a little bit of that sense of accomplishment tied to the story.