@de budding,
If you look at it from the perspective of the diamond system, you would seriously consider dismantling the system brick by brick. One matter of contention in the diamond system that I do not like is that the London diamond exchange holds a true monopoly over the industry. When I say true monopoly, I mean true monopoly. Get this? all legal diamonds go through the London diamond exchange one way or the other. That exchange has such a hold over the industry that vendors who sell us diamonds (USA, UK, Europe, etc.) buy the diamonds form the London exchange without even knowing what they are buying and what amount or quality they are buying in. They virtually hand over a blank check and hope they get something good. And if you go against the monopoly? you are black listed from the exchange and your company will go under.
Can you imagine insanity of such a monopoly?
But you bring up an interesting point about whether or not diamonds would be pointless without the diamond exchange. My answer is yes. But it is yes because of the fact that they withhold, or more precisely "forcibly ration" 80% of the world's supply of legal diamonds they receive, thus inflating the price of the common diamond. Art, I would imagine is the same way, except it is the attribution of the label "this is art" that is rationed.
But the issue of an alternative system is an excellent topic. What kind of system would work? I wonder about that myself. I will have to think on it, but I'm interested to hear your thoughts on better system.