[Meglobob]

Well I am against nerfing of clams, I do like the idea of the introduction of anti-clamming spells. So you have a counter strategy to clams.

A global that destroys 10%/per turn of all gem producing items in the world, would stop gem spamming abuse.

You could balance the introduction of such a global by reducing the cost of the gem producing magic items back to what they where in Dom2.

So the gem producing items where useful early on but not a effective long term strategy because there was a counter in the form of a global.

The global would after be relatively cheap, 40-60 gems so could be recast over and over to avoid it being just dispelled too easily.

The clams, blood stones and fever fetishes would still be useful as a mirco-management saving tool. Instead of giving a scout a pile of gems to refill your mages when they use there gems in battle. Just give him a clam or bloodstone or fever fetish to produce them on the way.