[rdonj]

GemGens still give you a useful and unique ability that no one else has. Clams allow you to perpetually, albeit slowly, replenish the astral gem supply of a given army, which can be handy for logistic purposes. Or just permanently boost the gem supply of your nation, if you really hate the idea of sending it out. Bloodstones are actually pretty good as uniques, being a very rare earth booster as well as the gem resupply purposes. The bloodstone is easily comparable to the ruby eye, for example, except better relatively due to the greater usefulness of earth gems and earth boosters being so rare. And I think that a clam of pearls is probably reasonably equatable to some of the lesser pre-existing uniques, like say igor konhelm's tome, or the headless hoburg :P

And of course, when you allow clams of pearls to be mass craftable, that is what happens and the most powerful person in the game is the person who has the most clams and the greatest capacity to forge them. Making them literally THE most powerful item in the game, greater than any artifact.