Not sure if you guys ever played Star Wars Galaxies, but you may have heard tell of the great resource and crafting system there.
Part of what made it great is that the resources you could find would directly impact the output of the crafted good... for example, to make a blaster you need "iron" but iron itself had a list of properties.
This means you could be in possession of really high quality "iron" for this purpose, and therefore supply a master crafter who could in turn make a run of blasters that were unmatched.
Until someone discovered a vein similar in quality again, that is :) But until then, regular every day iron was used for regular every day blasters.
Even then you could still choose to make an item out of a completely different metal either because it had different properties or you just happened to have it on hand.
That's where this really comes in - I would like the flexibility to create something that requires metal, out of any kind of metal. If it requires copper, or "requires" iron or copper, that takes a lot of potential choice and flexibility and ultimately customization out of it.
If I need copper, I'm now simply required to acquire it from Kingdom X, and that's it. I'd rather Kingdom X have the "best" copper for my application, but I could also choose too use local copper since I have it on and and need to keep costs down.
The current promotion of KSversary talks about the rare ingredient rewards in this way:
"These resources will be from a collection of unusual items gathered from distant shores or hard-to-reach ecotopes. Each ingredient has its own special properties that are passed on to any item they're used to craft"
So that gives me a little hope that resources from different areas will possess unique properties, which are passed on to the crafted output.
Or at least that resources can have their own properties :)