I could see that loan system to be very useful though.
During the planning staged of Braavos, I was going to make a player run bank with a loan system. It never got running due to the fact that loans are not enforced by staff, therefore I would get scammed out of a lot of moolah.
I had discussed something similar about the economy with Kainzo some time ago. My suggestion was based around the idea of the DHX being a stock exchange.
The unfortunate thing about a player run economy is that anyone can get anything. One of the few ways I make money is by simply not buying anything. It is difficult to maintain a player run shop as well because everyone undercuts EVERYONE, and in order to stay in competition, you have to spend 50c to remake a shop, which sometimes nulls all profits. A stable economy cannot be achieved when item prices do not fluctuate and players constantly drive prices down (exception for Gold Ore).
I also firmly believe in taxing sales.
Long ago I knew of a plugin that would fluctuate prices based on the stock in the chest (I have not looked into your link yet, but it looks similar).
All in all, I have always believed a free market in Minecraft does not work, and that Herocraft needs to stop focusing on PvP, and fix the economy.