Long term trade
Silver instead of gems
If you think that is very detrimental consider this: 28% of 50 cents per citizen that is 14 cents per citizen you lose versus gems. Even if we assume you are a VERY large nation of 150k citizens that is a loss of only 21k a day versus gems.
Wheat -
Fish -
Cattle -
Sugar - Captain Floop
Spices -
Pigs -
Water -
Lumber -
Aluminium -
Iron -
Marble -
Silver - Captain Floop