Experience boosters might work for alts. Buy heirloom consumables at max level only that give a certain percentage XP buff for an hour. Would help to power through some of the tedious parts of leveling alts.
However, currently the worst part is Pandaria. Great zones and quests, but the sheer amount you need to do is pretty grueling. Early on its fine to have to work towards level cap, but right now I think the whole continent could do with a small buff to xp gain. Maybe have it balanced so you only need to complete 3 zones to get to 90 now instead of 4 (was actually nearly 5 for my main since I completed green quests as well).
Also buff XP from doing dungeons. Its bad enough that there's no variety in the 85-89 bracket, but the XP gain is really low right now! I'd at least double it compared to what we get now, or make the dungeon quests much more generous so you're encouraged to do them at least once per alt!