I was thinking of something similar. Give them a reason to find other villages, map out trade routes, protect those routes etc.My players have calculated all the weekly income they have (they have excluded building material) from various functions. They have built a marketplace but there is also a friendly nearby village so we just assume that the goods are sold/bartered there. They have also (of course) added all the weekly cost. My players have a net gain of about five or six silver a week or so and I have told them that this is not money, they can pick from the goods that they produced to a value of their net gain. Simple, fast, just takes a couple of minutes to check and adjust the bookkeeping.