[Gothika]

That might work. Cutting the cost down the middle, Half ECs Hald Diamonds.
It would give Diamonds more a worth. These days they are only useful for preping weapons.

Also I've got another idea. This idea is a bit weird and most people will disagree with it. But what if they was a casino opened. (on Events island)
Where you buy chips. And Gamble to win points. And you can buy stuff with your points at the cash in. Stuff like: Diamonds, ECs, Gold Keys. ect..