I think the easiest way to add spying in game is add spy to hero trait "adventurer". After get experience by hero you can choose "spy", like now defense, wit, etc.

Spying could be only possible during hero war. Choose (new added) battle card SPY, and no use any weapon during this phase but you got a chance (10-50%) to get an enemy technology.

Chance will be depend from strong of empires (score points). If you are twice weakest from enemy you have 50% chance to get technology. If you are equal or stronger than an enemy you get 10% chance to get enemy technology.

This will help to balance game for weaker players.



DON'T HAVE TECHNOLOGY, THEN DON'T HAVE ARMY, DON'T HAVE CHANCE ... CHOOSE SPY :-)

I'm rpetty sure the devs have already commented on this and they haven't decided yet if they want to add it.