Crafting does drive gpot expenditure because crafting takes up ungodly amounts of inventory space. Mats don't even stack past twenty, which is sometimes not even enough for crafting more than one item. I've had mailbags go to more than fifty pages on crafting mats alone.
I think disassemblers have it worst because of the bounding effect, and because AH fees are murder on secondary markets. If they had the ability to buy, but not sell, bound items, it would be a big improvement. What are they supposed to do? Harass their own guildies endlessly and stand next to npcs to spam offers to buy leather and cloth at +50%? In game trading tools are so bad that it seems like there would be a lot of appeal for some kind of out of game app.
I would have thought a 50% penalty from npcs was adequately stiff to spur a little greed, but markets are troublesome to get to, and markups from AH agents can quickly eclipse that. Perhaps there should be designated crafting areas where people will naturally become congregated, and where other players can expect to go and have a decent chance of doing a bit of barter without drowning the whole sector in spam. Maybe crafters could be tied to npc anvils or looms. Maybe animal npcs could drop skins and humanoids drop cloth instead of eyeballs.
Likewise, crafters need to make items with stats as varied as those offered by quartermasters. Item improvement would also be a big draw.