I think an interesting way to handle / improve some of this might be to add "Ambassador" units which cost little to nothing to make and you can pump them out like candy, which you send to another city or government where they can perform in several ways:
1. Their presence ups the "good will" counter between you and the other city or country, multiplied (to a point perhaps) by the number of ambassadors so stationed and with perhaps an additional factor representing the amount of time they are stationed.
2. They can act like low-level spies / reporters generating information or maybe performing low-level spy missions maybe with higher risk of being caught. An interesting secondary function for them (perhaps an upgrade) could be the ability to perform low-level snooping or perhaps sneak in a low-level unit and hide it under the guise of "diplomatic immunity". The lower the level, the less likelihood of getting caught perhaps. Maybe that could be additionally modified by your government type.
3. If you send ambassadors and then declare a surprise war, they are summarily executed and some sort of noticeable gold penalty could be extracted per ambassador, and perhaps an unhappiness penalty per ambassador meted out for your civilization- just the thing you need at the outset of a war... If a war is declared more formally, or perhaps for which a causus belli exists, the ambassadors might have a better chance of making it out alive or perhaps deposited at the border or something. Maybe both nations would have a chance to remove or thin out their ambassadors prior to the outset of hostilities.
4. If you withdraw all of your ambassadors, that could be an immediate signal to the other city or country that something might be up and perhaps you would loose good-will points quickly, per ambassador. Otherwise, if you withdraw one or two, that could be a signal of displeasure to the other country and THEY would lose good-will points. So this could be used to help regulate behavior in both directions.
So the ambassadors / good-will points system could be used as an adjunct to diplomacy, troop build-up, and perhaps even international trading to help signal (or hide) intent and promote better (or worse) relations between nations-- and to provide some additional degrees of subtlety to international diplomacy. And as a reminder, they're not just throw-away units because their deaths represent an actual loss to their nation while their use can provide useful benefits and rewards. So while ambassador units might be cheap / easy to create and dispatch, one they are deployed, they represent a real risk / potential cost for bad behavior-- at least without some planning / preparation prior to taking some action.
My two cents ;-)
JWhitten
