The biggest barrage ive done was 7 ICBMs and a tactical against the French. The only reason i had those was as a deterant for their nukes.
Nukes arent that bad if you've got excess production just going to wealth, but otherwise its just not worth it. Also, if you want to capture the enemy towns, its best not to use nukes, as they will make most of the country-side polluted and
evil
I have found a nice use for nukes though. If you and a neighbouring civ are roughly equal, but you have the SDI wonder, a nuke barrage will definately knock the other side out of any chance for victory.