I'll weigh in here,
There is no right or wrong way to play.
Its very true, I run through 1 - 50 at least once or twice a year and that's enough.
Ive lost track how many times ive old school level progressed over the years, so to not run the game in the ground I do power level concepts in AE because I don't want a grind on everything.
I find building concept characters fun, I find endgame fun, I find old school level progression fun. But its like crops you have to rotate your crops otherwise you will burn out your soil and not grow anymore crops.
So I rotate the three - I'm currently running all end game for a few weeks - running the story mode praetorian war, Dark Astoria - then who will die and the pandora missions.
So I guess the end result is how best to live out your superhero fantasies vicariously through the game, or how best to number crunch and min max GenericAlt00765, or how best to hang out with friends and have a good time any way possible.
The game is pretty limitless on how to accomplish any of these scenarios, in any way imaginable.
There is no right or wrong way.