AnotherGame is a mod for ToE 3.1.

The difference is significant. Should I build a town hall for 5000, which provides a +1000 bonus to gold, or upgrade a gold mine for 7500?

I don't understand the point; what does the castle's construction time and the mine's output have to do with it? I'll only get 40 stacks of wood by the end of the period. Be consistent with the payback period – 7 days means 7 days, not 20.
In the case of the Elves (and I would never trade 7500 gold for 40 wood for other races), a lot of wood is only needed in the first week.