I did a google search and can't find nothing online except one post that said spies can bring down unrest in your cities. Do spies increase happiness in your city? Everything I find says they they make great security but nothing on how they affect your own peasants.
I have a city with high squalor and I had no general in the city so I focused on happiness buildings and a higher garrison of troops but then I thought maybe a spy would make my people more happy and purchased one but the next turn the happiness rating was still the same. I don't want to invest in a lot of them if they don't actually help my people. I know they are really good for other reasons and I am just wondering what they do for your own cities. If they can cause unrest or rebellions in cities of other factions can they not prevent rebellions, riots or even unrest? Do they help with happiness? Anyone that could answer this for me it would be appreciated.