I think for me the most enjoyable part of the game is playing different characters, powers, ATs etc. On my main I spend a bit of time on incarnate and endgame stuff just so I don't feel like I'm missing out on anything there, but to me it's mostly a lot of work that isn't worth it. If I want to get her fully cranked out I'm looking at hours more leveling for incarnate slots and salvage, hours planning out the right build, WAY MORE hours farming influence and buying the stuff I need to kit out those IOs. All for what .. bigger numbers on the screen? So I can farm +4/8 instead of -1/8? To me none of this compares to the enjoyment of getting even 1 new power when leveling a toon, or having a menu of different 50s I can play depending on my mood.
So I rush some of those to 50 so I get to actually experience those sets/ATs fully. If I'm being honest .. I also could really give a rats arse about story and content. I just think the powers are cool and I like to kill stuff.. especially en masse. I farmed my brute to 50 on the same AE mission over and over again, and as soon as I could handle /8s, I loved every second of it. I also love running in full teams filled with tons of mobs and chaos. As most here have said .. to each their own. That's the beauty of this game - there are SO many different ways to enjoy it.