I myself could care less about a lot of the in game achievements, such as holiday events, quests, first aid! and pretty much all others.
Now, I do not know why I loathe them so much but hey, I cannot stay focused enough to run around and grind rep so I just don't. My Fiance' however is what I call and achievement W***E. She will spend hours rep grinding, quest grinding, any achievement she can do she can and will, she completes holiday achievements the day its available and you cannot move her till she has that title to boot.
So, why is it some people can farm achievements, where others farm there brethren? Personally I can handle PVP achi's, Dungeon achi's and leveling proffs to max, but for my life, rep grinds and quest grinds just make me wanna log off. So, is there anyone who even aims at them all? Do you try for some to keep you interested? or like myself, when your bored do you decide to hand some Tauren his flank?
Whatever your goals may be, its good to have them, the nature of wow at 80 is a killer, you raid you farm, you get bored to tears and push through it. Having a goal to get, will make you much happier than 2 hours flying around northrend for ore. Try to get kill limits in BG's, rep grind in azeroth, or even see what your 80 can solo these days.
Have fun and try not to get bored.