I think besides the fact that spies can now fight well in the Recent patch. I think they should have another ability That makes a lot of Sense.
If a spy gets near certain buildings. The player will be able to see what techs of the enemy are being researched and units being trained as well as knowing where your Enemy Shipment location is set via an icon hovering above the buildings ONLY IF the spy is near them.
The Native and Asian Equivalents should have this too as i dont know what anti merc units they have. This will make spies more used in Supremacy.
However i think insane amounts of testing are needed as this might make them too good at supremacy to pass up.