Seeing as there are lots of pieces that are transmogrifiable and that many are unaware of which is which and if anything is held as valuable for said pursuit, I wonder if there would be an advantage gained by creating a character that posts Transmog auctions, with a name such as 'transmogsales' or similar so that the largely ignorant population might actually spend more than a second or two to examine said items whilst perusing the establishment, aka the auction house. I always go for the little mind games angle myself as it usually works.
I have perused the market myself and perhaps like your auction houses, it is pretty dead and requires much patience to get a sale but at this stage of an expansion pack, people are not interested in pimping their looks at all as they are still out there examining/chasing all the new gear. I would think Transmog will come back, but certainly towards the end of MOP so if you have the patience, the space and indeed enough money to not have to worry about your investment, it might be worth hanging on to the goodies for later sales. Having said that, the initial transmog craze will probably not be as big as before unless they change the dynamic, perhaps with the introduction of dyes and a higher degree of customisation on a piece which is arguably something not worth them pursuing, but I do think the dyes will come.