Agree that the ledger shouldn't list foreign assets. It shouldn't do so for the AI either, of course.
Perhaps a simple 90 day covert mission should be implemented for everyone that gives a brief assessment of the military strength of the target. Same stuff you might find in the ledger - a (rough) estimate in number of troops by unit type and manpower reserves. Maybe even throw in army tradition, discipline, and morale statistics to boot.
Also, a case could be made to have two additional idea groups implemented that are based on espionage. In addition to having one in the diplomatic stream, groups in military and administrative could also be considered.
Military espionage could possibly do the following:
1. Enhanced Intelligence: Gather even more details about enemy troops, including their movements (persistent with diplomat on mission)
2. Disinformation: Upon enemy spy discovery, allow the player or AI to alter the disclosed information if desired (static ability)
3. Diversion: Create ghost units from existing units in friendly territory, which turns existing units invisible until "ghost" is attacked or existing enters enemy territory/attacks (triggered 10MP ability)
4. Propaganda: Increase enemy War Exhaustion (persistent and increase over time with diplomat on mission)
5. Sabotage: Destroys 1 level of fortification in a selected province (1 year mission)
6. Targeting: 25% increased chance of killing an enemy leader during battle (Passive ability)
7. Tactical Advantage: Remove 1 level of tactics from opposing army (Persistent with diplomat on mission)
*shrug* lots of stuff that can be added. Perhaps they're waiting for a DLC
