I liked your connection points for prestige in an MMO and I agree with you. Black Market AH imo is a really odd thing to put into an MMO, and even though I did and still do believe gold is equal 'effort' per say, it can't and will never deliever on prestige like you discribe so well.
Seems like it is suppose to be a gold sink for the richest of the rich and for those that can camp out the AH for when it finally reviels itself. But I think the key point is how often do these items appear, how much do they cost, and is it perdictiable. I mean if Ashes pops up once a year, for 200k gold, and appears at a completely unknown time then it really doesn't make to much of a difference. But if every Tuesday a new Ashes is up on the black market and its 100k gold then it is suddenly a peice of prestigless junk. At least in my opinion.