I have an idea for a way to increase opportunities in the game to find / earn diamonds.
In the Games section, a new subgame called The Mine.
It would require a Dwarf team and a pickaxe as a weapon and it would reset every day. Every level of the mine you complete takes you further into the mine… the mine levels would typically grant shards as rewards with each mine level granting the possibility of the discovering rarer gemstones.
Players would need to earn / use gems to buy the pickaxe, which could be upgraded per the new weapon evolution tree, with each weapon bonus adding things like 5% bonus chance of finding diamonds, 110% shard discovery, reduction in cost of forging shards into diamonds, etc.
I feel this way every player would have the opportunity to bust their ass to collect the shards to improve the rate at which they gain diamonds, etc., without imbalancing them as a currency or making them solely discoverable by the power players.