I think we should be able to buy gems with coins that we earn playing ourworld.
How it would work is:
1> We can go to the store
2> There is a place in the store to buy gems
3> We choose the amount of gems we can afford(with the coins that we have)
4> We spend our coins and earn the amount of gems we paid for
But not make it so costly that you can get 5 gems for 10 mil. Something reasonable like 10 gems for 1 mil, and so on...