To fix espionage system, we have to figure out how espionage will be useful to us in the game.
If we know what the enemies are doing comprehensively, then we will know how to adjust our actions. For example, if we have access to what wonders are currently being built, we will have a good idea of what wonders we should built and what to not bother with. If we have an idea of the enemy city's productions are, and we learn that 3/4 of the enemy cities have been building military units in the past 20 turns, we will have a good idea that a war is about to break out, and we'll know how many and what kind of units are we dealing with. If we can use espionage to clear fog of war, we will be able to plan our invasion by knowing which city is very far from concentration of military units.
Right now Civ espionage system as it is gives us piecemeal intelligence that are pretty useless. I think espionage system is designed to give us players ability to do something, such as, for example, steal tech, sabotage, and tweak election results. This "action" mentality however must be balanced by required restraint not to empower spies to such an extent that spies can do too much sabotaging, thus making it unplayable. Image playing a game where your production is constantly being sabotaged. What fun will you have playing such a game?
My solution is to simply drop the "action" mentality. Spies don't need to have to be able to do anything other than simply collect intelligence, and doing so in such a way that it gives us comprehensive intelligence instead of piecemeal intelligence. Some features allowing sabotage is great. For example, if I really want to built United Nation badly, and I know that Beijing is six turns away from completion, I can sabotage its production so that it will need 10 turns to complete it, thus giving me more time. In the meanwhile, I'll send a caravan and hook up one of my cities with the other one that is building United Nation wonder. But as have been said, sabotaging shouldn't be allowed to such an extent that we can abuse it. Remember, what we can do to others, others can do to us, too. Imagine when we are on the receiving end of the sabotage constantly. It will make the game miserably unfun to play.
There are two kind of strategies. One is optimization. The entire Civ game is designed as an optimization game, where we figure out how best to increase efficiency of our economy. The other kind of strategy is where you adjust your moves based on enemy's move. Sometimes, this result in sub-optimization, but it will give you an advantage over your enemy. This second kind of strategy game requires intelligence, which Civ espionage system as it is now is woefully inadequate to provide. For starter, the fact that I won't get a spy until renaissance makes this whole system useless.
Here are some specific features that may make spies more useful:
As soon as writing technology is discovered, we can recruit spies by building like we would built any units.
New city improvements can improve the functioning of spies just like marketplace can enhance gold output, or factory can enhance hammers.
The more oversea trading we have with another civ, the more accurate spy information will be.
A spy will be able to hide out anywhere I want it to. The location that it is stationed at will allow it clear fog of war for that region. How big of a region can the fog be cleared is up to designer.
A spy will be able to hide in the capital city and bring back report each turn of what all the cities in that civ are building. But information isn't always accurate. A higher level spy (higher level perhaps because it was recruited in a city that has certain spy ability enhancing improvement built, or because of accumulation of experience points) may bring back more accurate information. Alternatively, a higher level spy may not only tell us what they are building, but also how close are they to finishing it.
A spy in city states will give us a picture of the influence that each known civ has on that city state.
The thing to do is to reflect on how most players play Civ game, and figure out important elements of our optimization strategies that are commonly used by Civ players. Then figure out how we can implement spies in such a way that it will tell us how enemy civs are progressing with execution of this optimization strategy so that we can adjust our moves. That's all spies need to do. It doesn't need to be empowered with abilities to sabotage or do anything actively. It simply needs to passively collect intel that we will find useful.
If we know what the enemies are doing comprehensively, then we will know how to adjust our actions. For example, if we have access to what wonders are currently being built, we will have a good idea of what wonders we should built and what to not bother with. If we have an idea of the enemy city's productions are, and we learn that 3/4 of the enemy cities have been building military units in the past 20 turns, we will have a good idea that a war is about to break out, and we'll know how many and what kind of units are we dealing with. If we can use espionage to clear fog of war, we will be able to plan our invasion by knowing which city is very far from concentration of military units.
Right now Civ espionage system as it is gives us piecemeal intelligence that are pretty useless. I think espionage system is designed to give us players ability to do something, such as, for example, steal tech, sabotage, and tweak election results. This "action" mentality however must be balanced by required restraint not to empower spies to such an extent that spies can do too much sabotaging, thus making it unplayable. Image playing a game where your production is constantly being sabotaged. What fun will you have playing such a game?
My solution is to simply drop the "action" mentality. Spies don't need to have to be able to do anything other than simply collect intelligence, and doing so in such a way that it gives us comprehensive intelligence instead of piecemeal intelligence. Some features allowing sabotage is great. For example, if I really want to built United Nation badly, and I know that Beijing is six turns away from completion, I can sabotage its production so that it will need 10 turns to complete it, thus giving me more time. In the meanwhile, I'll send a caravan and hook up one of my cities with the other one that is building United Nation wonder. But as have been said, sabotaging shouldn't be allowed to such an extent that we can abuse it. Remember, what we can do to others, others can do to us, too. Imagine when we are on the receiving end of the sabotage constantly. It will make the game miserably unfun to play.
There are two kind of strategies. One is optimization. The entire Civ game is designed as an optimization game, where we figure out how best to increase efficiency of our economy. The other kind of strategy is where you adjust your moves based on enemy's move. Sometimes, this result in sub-optimization, but it will give you an advantage over your enemy. This second kind of strategy game requires intelligence, which Civ espionage system as it is now is woefully inadequate to provide. For starter, the fact that I won't get a spy until renaissance makes this whole system useless.
Here are some specific features that may make spies more useful:
As soon as writing technology is discovered, we can recruit spies by building like we would built any units.
New city improvements can improve the functioning of spies just like marketplace can enhance gold output, or factory can enhance hammers.
The more oversea trading we have with another civ, the more accurate spy information will be.
A spy will be able to hide out anywhere I want it to. The location that it is stationed at will allow it clear fog of war for that region. How big of a region can the fog be cleared is up to designer.
A spy will be able to hide in the capital city and bring back report each turn of what all the cities in that civ are building. But information isn't always accurate. A higher level spy (higher level perhaps because it was recruited in a city that has certain spy ability enhancing improvement built, or because of accumulation of experience points) may bring back more accurate information. Alternatively, a higher level spy may not only tell us what they are building, but also how close are they to finishing it.
A spy in city states will give us a picture of the influence that each known civ has on that city state.
The thing to do is to reflect on how most players play Civ game, and figure out important elements of our optimization strategies that are commonly used by Civ players. Then figure out how we can implement spies in such a way that it will tell us how enemy civs are progressing with execution of this optimization strategy so that we can adjust our moves. That's all spies need to do. It doesn't need to be empowered with abilities to sabotage or do anything actively. It simply needs to passively collect intel that we will find useful.