I can relate to everything you said. I played all the way to Pandaria but I got tired of grinding hard only to see a new expansion come out and all my gear become worthless.
I don't like playing just to pass the time, either I can be one of the best (top 20%) or I prefer to not play it at all.
I was more of a casual player, so it was not too bad for me. I knew I was never going to be at the top, so I just enjoyed grinding away and collecting mats and stuff.