Add a feature where you could upload a masterpiece with a price of Diamonds.
Why not have a use for Diamonds?
People probably want to get rid of them.
What people would like is using diamonds as economy to buy other users work. I'm sure some uses don't want to given there master piece away for free! Many users work gets stolen as well. if you use diamonds as economy it will stop people from stealing other peoples stuff. for instance Someone stole my map and I uploaded it with a price. People would say that they have bought that map before!