AlphaShard
Emperor
I can see your argument, but at the end of the day it's a judgement call. Personally I think the information has more diplomatic value when given away than it has practical value when held back.
I agree the Diplo value far outwieghs the practicallity here. Honestly this feels like a free +1 "Oh wasn't that nice?" After all they didn't have to tell us at all about their Gems for quite some time to come. Not that it gives us an advantage but it puts people in a "Friendly" mood.