Paratroopers are also good recon units. Type 'p', then move the cursor all around the area before you actually attack. If you can't land on that tile, it is occupied. You don't know by whom or how many, but it reveals troop positions.
I don't use nukes in my games (I will even go to great lengths to sabotage any Manhattan Project), so I will often use paratroopers to recon and secure my path to the target city. Drop them into a fortress or mountain and kill whoever is standing around.