From my perspective, I've given up mostly on collecting mounts/pets because they add so many bloody new ones each patch that I get tired from trying to farm them all. You basically need an army of alts or multiboxing to have a feasible chance of obtaining all the mounts/pets. It's similar to how I used to get every achievement in the game, until WoD when they added that insane amount of archeology achievements that just seemed to be there to make you do archeaology 20 times longer than necessary, so I stopped bothering after that (and this is coming from someone who did the Insane in the Membrane achievement the first month it originally came out). None of it feels special anymore, as everything feels like more of an chore than an experience/achievement. That's the feeling the OP seems to be describing: killing a rare used to feel special/meaningful, now it's just a chore and a daily quest.