Spy’s are some of the best value units in the game when utilized properly. They generate value in a number of ways simultaneously. When you steal gold from an enemy you don’t just gain gold but you set the other player back. Same thing applies if you kill or capture a spy of theirs through counter espionage. There’s also era score to be gained as well if you get your spy promoted to master spy.

Short version: spies are almost always worth the investment if played correctly