The rewards are VP based, but the stone amount is a quarter of the amount displayed in the VP chests.
For example, I at 1000+ VP get 8 shards per chests, but from the Warship chests I get 2 shards per card, up to a max of 4(2 cards giving 2 shards of separate color).
Personally, that's more than enough for me. Consider what else you get that gives you stones. On top of regular raids, you get 3 guaranteed frags from auto-destroying NPCs, you got Dr.T, Megacrab and even Hammermans Imitation can be considered. Even the stone chances can be boosted from Tribes so you don't even need PSC. I certainly don't and I am consistently going up in powders.