In a more general sense, looks like resources are the key to identifying good ways to specialize a province. Grain obviously helps food production. Haven't really looked, but I suppose iron and timber probably help industry. All resources will boost income to some degree, at least through trade if not some more direct bonus.
Tapping one of the better improvements suggested in another thread...how cool would it then be to have provincial resources tied to industrial capabilities (iron>smithy; cattle>leatherworking; timber>shipbuilding, war machines; marble/stone>advanced building structures, paved roads; etc.

Tie this sort of thing together with diplomacy (I'll trade you my iron for your marble, etc.) and trade partners/alliances might actually come to be far more important than they currently are