The idea of this sugession is to add a quality tag to raw materials.
Trought history, many site and town have been famed for the quality of their handycraft. We can think of Dama's steel, ancient Roman's Terra sigillata, french wine, belgian dyed wool,...
The quality of these goods come from the talent of the artisants that have dedicaced their live to their work, but also from the exeptionnals raw material aviable in these area : dama's iron is suspeced to have had natural durcissor in him, the best workshop producing the ceramic had acces to hight quality clay, french soil and weather is ideal for the producion of great grape, and the quality of the wool greatly depend of the quality of th water she is waashed in.
In itself, seing this kind of phenomenon in Df would be great. But the implementation of this fact in game would be a great invective to trade with the caravans, and, as soon as we are able to do something about it, to open new traderoutes : wouldn't it be awesome to be open a traderoute to Awardenong "the evilness of gerbils" to be able to import a bit of his Iron ore at great cost to make the absolute best steel sword to fight the clowns menacing your forteress before you dig deeper ? To get a hold of a bit of that fabled sunshine produced by the elven of ... in ideal soil?
This mechanism probably wouldn't be opressive : sure, Dama's steel was said to be the best, but it was not an overwhelming advantage in fight provided you have another masterfull weapon. In the current combat mechanism, an additional bonus of 5% at best seems reasonable. Of course this have to be tought in each case so it would be something a player may want to care about but wouldn't have to.
Do you find it an intersting idea?