[Baron Munchausen]

Interesting proposal, but lacking in one crucial aspect -- politics! There should be influences from the state of 'unrest' on each planet, the species inhabiting the planet (if it's your 'original' race or a conquered species or a species representing another uncounquered empire!), and the dominant species of the empire attempting the intel operation. Essentially, both individual planets and 'species' will have unrest or loyalty Ratings. Not only can a given planet be in an unfavorable 'mood' and make intel operations more likely to succeed, but an entire species of an opposing empire could also be in an unfavorable mood and highly disposed to aid enemy intel operations. Planets inhabited by your original race would tend to be more loyal and so more difficult to carry out intel operations on, of course.

Implementing this properly requires some unrest 'modifiers' based on the relations of your empire to the 'original' empire of the race(s) on your controlled planets, and level of unrest for other reasons, and how you deal with it (fix conditions causing unrest or just land troops?) and a few other such things.

Combine this with some modifications to the way troops affect a planet -- first a slight reduction in the chance of intel sucess per troop, capped at some reasonable level so you can't make completely immune planets by piling on hundreds of troops, and second that troops should remain loyal when a planet rebels and attempt to put down the rebellion (fight the militia essentially), and you've got some really interesting situations possible.