Spies can be used to: 1. Sow discord between two civs making their relations deteriorate 2. Sabotage, damage a building, making it useless for a few turns. (When caught leads to declaration of war). Diplomats shouldnt be just schmoozing. A city with a diplomat can improve trade route yield (more gold and science). cultural exchange (+ culture to the trade route). Diplomats improve relations gradually and wears off past grudges more quickly (counteracts spy's sow discord). Right now it feels like the only way to bring down a runaway is to go to war. Espionage should provide alternatives. E.g. you can sabotage space ship factories, key tourism buildings. You can sow discord and convince other civs to stop trading with him.