How about having the first tier giving you +1 line of sight on borders. For example if you had the level 1 espionage tech you could see 2 spaces from your borders. But only the units right next to you could have full intelligence, the units deeper into enemy territory would just tell you like 1-3, 4-9, and 10+ as intelligence without telling you the exact strength of the unit.
Also i liked the idea for an 0SS, Skorzeny, Commando, etc. type unit. It would deploy like Garrison forces and couldn't retreat in battle, but it would be totally invisible. It also couldnt be reinforced. Say for each unit deployed dissent goes up for some formula depending on belligerance, society structure, etc. IT would be tilted so that closed highly belligerant societies would be extremely hard hit and open peaceful nations would be only lightly affected. The only way to stop these commandos would be to use garrison units in anti-partisan duty. However these units would have a small max strength like 1 but only have a 5% chance per day of being engaged by the garrison.