ok there seems to be a bit of a confusion (well two confusions) first:
many people confusing personal money with global economy...this has been addressed so i will simply note it here,
the second: people confusing MONEY with WEALTH.
gil can be used to buy things, ok we all get this concept. but the thing you are buying is the point, not the gil. so for instance DoL and DoH are constantly generating WEALTH (i have HQ everything for instance and that is stuff i didn't have to buy, and were they not bound i could conceivably sell for gil, it is wealth) though not MONEY.
now if players could do everything there would be no problems, player would give player money for wealth AH would take some money out of the economy, the economy would decrease in overall money driving the cost of goods down and the same amount of wealth would get moved around.
the main complication happens when NPCs with their fixed amount of costs enter into the equations. no mater how the economy goes dark mater costs the same, and things the NPC sell remains the same. when it takes too much to keep your character up it's not worth it to generate wealth into the economy so people don't.
what can be done:
one: make dark mater mine-able and allow users to offer repair services. this is a source of wealth, it is a service which can be exchanged for goods independent of gill.
two: let people sell goods on the market that they have bound to. this adds fungibility to this source of wealth and encourages resell/hand-me-down
three: allow barter on the AH.