I think this is a question that needs to be looked at a bit more closely in every game. Take Warcraft or Wildstar and their End/Elder game respectively. That's the main reason people play them. Most of the loud dedicated players want raids and dungeons. People constantly skip leveling content, they power level, buy guides, skip quest text, fly over mobs, avoid as much unnecessary work as they can and find the path of least resistance.
Yet every expansion needs more leveling content, with better questing, and larger areas...
To what end?
Don't get me wrong, the vast majority of players will love going through it....the first time. And then we're back at 'end game.'
Part of me thinks we should stop dividing our MMOs into two separate game, leveling and end, to create a more constant experiance.
But then I guess that's what sandboxes are for.