For Crusader Universalis, we were planning on putting together a two-stage economic system of raw resources (similar to EU4, they are geographically-based, however we wanted to give some options to represent the persistence of monoculture under certain Kingdoms and how that weakened some medieval economies); as well as the second-stage refinement or manufacturing of those goods for final sale.

In this system, every barony would have a max of maybe 3 resources for players to pick from, with some form of grain almost always being available for food/agriculture baronies. Every barony would be restricted to just one economic building, which would be either a resource allocating building, or a refinement/manufacturing building which could be upgraded to allow for more resource input (so players do not need more manufacture/refinement baronies, reflecting the propensity of medieval kingdoms to concentrate into fewer, denser cities). For example, a thriving Kingdom of Sicily would have a number of varied agricultural buildings throughout Sicily and Calabria, with a high level agricultural refinement building in Naples. This is referencing the heavy and simplistic 'economic dualism' of medieval economies as well as allowing for supply and demand.

Many European Kings wanted a lot of grains for their armies and food, however their lack of familiarity with the way supply and demand works resulted in oversaturation of grain in the markets and a decline of many feudal economies; such as the aforementioned Sicily's. So in gameplay terms with the same example, you had a 'player' invade Sicily, replace all the varied agricultural buildings (olives, grapes, misc fruits) with almost exclusively grains, leaving one of the most prosperous places in all of Europe turn into a 'backwater' by the 14th century.

A merchant could then take advantage of this economic system and move products not based on a fixed value but rather supply and demand; buying these overproduced grains for next-to-nothing, selling them in the middle east and/or south Asia, and returning with luxury products such as silks or incense to then sell in the European market.

If you emphasize these mechanics, you won't have to emphasize mechanics like 'bandits' or 'pirates' to compensate for a lack of gameplay nuance.