Well, I'm going to be contentious.
While I can just about see value in preserving a few warships or other vessels that have significantly interesting interiors, I really can't see the point in preserving liners where the only real interest is the external appearance. It's basically a box of (small) rooms inside. I'm sure there is the odd item of aesthetic value inside, but they are really just floating hotels.
For my money (literally), with a few exceptions like HMS Belfast or some other historic iron (eg. Mallard), if a large vessel, loco, aeroplane, etc, can't be 'preserved' as a working item then it's probably not worth the cost of keeping it at all.
People will say "Oh, it's history" but they aren't usually at the front of the queue to donate ££££s to the cost of upkeep of these things. Expecting a commercial company like Cunard or 'the government' to cough up cash for these projects is ... well ... unrealistic.