When the news broke that patch 3.2 would bring new chest heirlooms, with a stacking +10% XP bonus, one commenter made an interesting suggestion: get heirlooms for your level 80 characters, and bank them until the next expansion. So far between chest and shoulders you've got a +20% bonus to all XP right there, and having some quality equipment always helps the leveling process.
Of course, there's every chance that Blizzard will simply disable current heirlooms for characters past level 80, to prevent precisely this behavior. They've done level-based nerfing before, with items like the Riding Crop and enchants like Crusader.
The whole fate of heirlooms in the next expansion seems pretty nebulous to me, actually; will we need to go back and farm Emblems of Conquest at level 90 to gear up our alts? It's too early to tell. For now I would hold on to any extra badges you might have, but when the next expansion nears, you may be able to make good use of them.