Yeah, I know the title's probably just landed me on a list, but the option to use one's spies to terrorise civilians is really overlooked in this game. According to the wiki page (which is reportedly outdated, but I'm assuming there's been no major rework of this particular feature), at 60 spies against 0, it will deal a mere 34.5 units of infrastructure damage. Even in the best-case scenario, this is clearly not viable as a method of attack, nor is it cost-effective.
I'm not suggesting an infrastructure damage buff here; 34.5 units of damage in a 2000 unit city translates to 1.725% of the city destroyed, which is far more than what the worst terrorist attacks in history have done in the real world. What I am advocating is the ability to destroy powered non-military improvements. I still haven't decided on whether targeting specific improvements would be too OP or not, but if targeting was implemented, some improvements should pose varying degrees of difficulty (a stadium is much harder to destroy than a supermarket, for example).
I'd be happy for this to be implemented, even if terrorism no longer did infrastructure damage. Although destroyed improvements would be easy to replace in peacetime, it'd certainly add a more dynamic and unpredictable aspect to wartime, as one may need to rebuild infrastructure destroyed in war before rebuilding any improvements, giving militarily weakened nations the opportunity to properly sabotage the enemy, as in reality. However, this has the potential to be very strong, so it'd be necessary to make it high-risk.
I don't have much experience in balancing mechanics, so this may not be the best idea. If you have any suggestions, I'd be happy to hear them!