I think that spying can be more better and i see that spying is not presented good in strategy games.

I suggest that a player can make spy network and spy network is made by sending operatives or can do special programme which involves local population.

These population can be used for doing revolution, sabotage, steal tech, etc.

These operators will make branches and also connect to other operators which make greater network.

Agent can also be sent to increase speed of task.

More than 1 operators can work in one city  but these can help in facilitating nearby espionage.

Intelligence pact can be done in which two civs can do joint operation.

To protect ouerselves player has to make powerful network which can expose other civ network and can launch a counter to eliminate enemy intelligence.