One thing I keep hearing is that people are distressed that all their hard work is going to be thrown away, when the game "resets" everyone for the climb to level 80. This happened when the first expansion came out, and a lot of people quit.
Here's what I tell them:
If only real life was always that simple.
I made a decision before I bought WoW, based on my experience with other games.
When I wasn't having fun, I wouldn't play. I wouldn't play in hopes of having fun later, I'd always aim to be having fun at the time.
If that meant progression, fine. If it meant playing 5 alts in rotation, fine. If it meant PvP, fine.
With that kind of attitude, there's no angst over a new expansion coming along and "ruining" what you've accomplished. You were having fun the whole time, so you got your money's worth.
Speaking of real life, three miles run today. Progress!