A step forward was done: armies use more food and special resources (all of them) boost the fighting capabilities of the armies.
Still is not enough, since not include the trade between players.
Wood and stone are pretty much useless, tons of each can be found in each province.
I don't have any bright idea, all I know is that players love to trade the resources and a trade system between players will be much more attractive than trade with a tech shire market.
Also, making available the special resources in a world wide trade system will generate more conflicts, leading to wars on economical reasons, not only religion or sympathies, making the game more realistic.
For example, the crusades had an important economical factor, an attempt to take over the trade with Orient (silk, spices and other luxuries) from Arabs.
Later on Venetian reach their moment of glory by sizing a large part of this trade.

In my opinion we don't need codes of conduct and police, but an economical base of the conflicts and a more attractive game for all the players, implementing a player vs player trade, like national markets with auctions, trade agreements and so.