To augment the seemingly impossibly thick armor and those famous mammoth 16" guns, the Navy outfitted the modernized Iowa-Class battleships with some REALLY cool 'toys' that were not available during WW-II, or even the Vietnam era: things like four Phalanx platforms to help assure that no anti-ship missiles would get even within a few miles of the ship, never mind testing its armor; Harpoon and/or Tomahawk missiles; and modern electronic tracking/monitoring/countermeasures equipment.
When the modernizations of the Missouri and her three sister ships were completed they were most definitely not "your grandfather's battleships". Even today I would doubt Iran has anything in its arsenal that could cause them significant harm.
It is my understanding that the Iowas had to be decommsioned because their hulls were thinning due to electrolysis. Building a new BB with modern gunnery with be very expensive but modern 16inch guns could I am told hit targets 100 miles away. Something to think about.
They can still fire the 16 inch guns, good for 20-22 miles but the real whoopass could be launched from > 100 miles out.