I've been coming back about every three years since I gave up the grind on my original account. After the beta they had double xp for two weeks, y'see, and my computer had died just in time to miss it. I got back in weeks later, but I felt like I had missed the boat. Got to the 40s, and just kinda stopped to do better at school and other pursuits. Each time I come back, I'm a bit more confused and a lot faster at leveling, to the point that the vast majority of content seems entirely pointless.
The game just needs more focus on cooperation. Don't even need new content, just raise the scale and rewards on old party content. Boom, you hit nostalgia and relevance in one strike.
