"Useless" Resources?

[kaffis]

So, when I read Higby's recent comment about three of the four resources having different uses for different empires, I had an interesting notion.

What if each empire had one resource type (which was different for each empire; so each resource is "useless" for one empire) that provided no immediate, tangible benefit to the empire?

That is to say, what if each resource was simply "left in the ground" by one empire or the other, rather than being harvested and spent on equipment?

It would still be indirectly valuable to capture and hold that resource, simply to deny it to the other empires, but would provide no direct benefit to empire X to hold.

Could this be a fun component to the resource system? What, if any, advantages do you feel this could prove to provide? What are the disadvantages? Discuss!