As anyone on a RP server (not me) can tell you, stats become obsolete, but appearances are forever. The funny hats, fancy robes, strange weapons, they are eternal. Or at least until Blizzard reuses the model. But still a BoE is more valuable than a BoP that people need to quest or raid for.
This leads me to Gnomeaggedon's woe: Got a pile of Tankard o' Terror. Shame there are 300+ on the AH already ranging from 13g to 700g. Hello vendor, can I exchange for a mount?
13g? Really, 13g? That supply will never grow once Brewfest is gone. They will go up in value. Not for the stats, and they aren't going to be selling for the thousands that they once sometimes did. The stats are outdated now. There's not so much demand anymore for a BoE 226. But for a giant mug that you can hit people with, that never goes out of style.
So if you see them ridiculously cheap and you have some spare bag space for a few weeks, maybe months, buy them up. Worst case scenario your shaman alts will look badass for a couple levels.