Nuclear weapons will rarely get used by the AI if you don't nuke them first. And you want to make sure that you only nuke them if you have too, and they don't have an arsenal themselves. There are some exceptions like if you are playing against Monty and it's on a level above Noble I notice he will use nukes, unless somehow you were able to get on his good side, even though he still might not like you. For example once I was the same religion as him, and even though he had nukes, and I was the aggressor he never used them.
However, I actually think that the nuclear weapons in the game are not that fun to begin with. I think this is one area where realism might actually make it more fun. Depending on what direction you chose to go with it. Spreading to 32 squares sounds a bit too much.