I was wondering about some of the buildings that provide + and +. It is possible to have the gold part obsolete before the building does. The represents real wealth in the ancient era but as you progress the wealth aspect should decrease. I am not sure about all of it an example may be the "Hunter's Camp", I can't remember when it goes obsolete/is replaced but perhaps the gold part could reduce at trade or something similar.
I am about to revamp all the herd buildings to have them evolve throughout the game. For example the deer herd will provide +1 , +1 and +1 to start with +2 at tool making and -3 at iron working to represent the usefulness of antlers as picks which are eventually replaced by metal picks. The food and gold will also change but not as dramatically.
So deer herd will wind up with negative hammers? Zero makes sense but why negative?