1. Make levels feel meaningful again. Getting a bunch of passives as one levels up (or spells they'll never use) feels boring. Talents used to give the player some interaction every level, but those are now reduced to once every 15 levels. Look from the perspective of a new player - no reward for leveling just means that levels really have no value anymore, just the end level. Revamp the talent system. Revamp what players get for leveling.
1a. The power levels at lower levels are ridiculous. Players can solo "at-level" raid content. Dungeon content is so trivial, nobody really puts in an effort. The difficulty of any instance pre-85 is lower than LFR. Its no wonder why some players feel lost with their character when they level cap.
2. Reduce the dependence of logging in every single day. Flip some of the dailies to weeklies. Introduce a reputation system that gives a % of the missed reputation for the day as "rested reputation," capping out at the daily maximum possible earned. The goal: get the players to not feel penalized if they miss a day or two of dailies.
3. More instances (dungeons, mostly) in expansions. Mists gave players the lowest amount of 5-mans in any expansion. When players are finished with dailies (as when their rep bar maxes out), they are so sick of them and head for heroics. After seeing a huge decrease in heroics (Cata had 14 at the end of the xpac, MoP currently has 9), they start to get boring.
4. **crazy, off the wall idea** Create "challenge" or "contest" servers where you could hold contests outside of arenas. Have one for speed goals and give out bind-on-account rewards for players that complete it under a set time (along with participation rewards). Another server for the first guild/group to clear content with cookie cutter characters/specs/gear. Hardcore PvP servers (where the character can't log in after dying, but gets a free transfer off server) is another possibility - something to get players playing WoW in a different way. To free up hardware for these servers...
5. Merge some servers. I don't care if you say that you increased server capacity and you want to make larger communities or if you just want to cut down on physical server space itself, it should be done with some servers that have identical types and time zones. Low population servers are no fun for quite a few players, especially if they are financially unable to fund a transfer.