I know that if I'm playing against a person with nukes I always spread my armies out to stop them from wiping it out in one turn, same with the air force in forts and carriers. The collateral damage from a powerful air force makes it easy to kill units and I get exp for my armour. The same units can be used over and over and over again. With nukes mostly used for hard points or massive stacks
I understand what you mean, if i have a good production and if i'm on par military wise with the civ i'm fighting, i use nukes only to kill massive stacks.
BUT, with nukes, you can win even when you are small and insanely weak military wise. I already take down several gigantic powerful immortal ai with three units and a lot of nukes.
First, switch in universal suffrage, raise your science down to 0 and rushbuy tac nukes (Considering your production is weak)
Every game, i save my great generals in order to create a few commando 2 move units in the late game (modern armor, or even cavalry, it works).
Then, let's the fun begin.
Like Tmit has stated, you can raze all their coastal cities in one turn easily with submarine and transports. But it's harder when your targeted city is inland. What if the ai is 10000 times stronger than you? You won't reach them. Too bad, when you have to raise a capital inland to prevent an ai to winning by space/culture/diplo...
Luckily, you have your commando units. Two scenarios:
1- You can nuke this city directly from the sea with your submarine or from another city (your city or a city of a civ who has open borders with you)
The, simply nuke and use your 2 move commando unit ( with rail road, if you have open border with a civ near your target, you can reach almost every city, almost...) and raze.
2- Harder, you can't nuke your target city because it is out of range (or out of reach of your commando), so you have to take another city (ot two if you are unlucky) before, a city which is not too far from your target city.
Let's say you want to raze Paris but you can't. So you nuke Lyon instead, you take the city with your commando (but don't raze unit).
But now, you have to wait one turn to rebase your nukes to hit Paris. If your ennemy is much stronger than you, you won't keep Lyon, even one turn. So? I give immediatly the city to another neutral civ which have not open borders with my ennemy (Bribe it before).
You see? I give Lyon to these nice indians. Napo can't reach me. I rebase my nukes and hit/raze Paris the next turn. Game over. You can also repeat this tactic until you have killed all Napo's cities. When you're in one city, you can usually raze three or four of them each turn it you have enough commandos.