So, I was thinking the other day of one more thing I was planning: switching mains. We've discussed the art of switching mains a bit before, but there's always a lot of hassles to it: there's the concern that you'll fall behind your friends, the concern that your gear won't be good enough, the concern that you'll have to grind your reputation up for certain keys and essential reputation rewards all over again.
A new expansion is just the ticket for getting rid of most of those problems. As long as your character is max level at the start of WoTLK, they can catch up on gear pretty quickly just from level 71 greens and quest rewards. Everyone's starting out grinding all the new WoTLK reputation grinds, so no worries that you're behind on those either. Despite being on a relatively "new" character, you'll be able to join your friends in Utgarde Keep right away.
So the reasons not to switch mains mostly manage to resolve themselves when a new expansion hits, and the question becomes, do you want to switch mains, and why?