You must realize that when NCL supposely claimed to have owned the SS United States, they wanted to replace the entire engineroom with a new disel plant, which would wipe out the ship's history. So far, they haven't done anything to the Big U. They never will.
You comparing the Big U to a warship, which it's not. If the ship can be refurblished into a 5-Star Hotel and Museum in NYC, It'll do very well because the hotel portion of the ship would generate revenue, as well as a small maritime/hotel/cullunary training academy onboard.
As you might have seen, most of the steamships are going to the scrapyard, because its much cheaper to build a new ship at the moment than to maintain an old one, thanks in part to the easy access to new fiancing(loans). But I have a feeling that all the building of new ships that we've seen will slowly come to an end because it'll cause an over stuation in the market, and some of the cruise companies will have a lot of debt that they can't pay off on time. Because they will be too many ships going after the same type of passengers, their profit margins will decline or stagnate.