Of course, though preservationists do achieve some great results with things that are not always 'much use' - eg full restorations of Victorian carriages rescued from being beach houses, when you could simply use a Mk1 instead. And come to think of it, preserved TPO carriages are not much use, since preserved railways don't carry post - as it were!
It would be great to see at least 1 or 2 Mk1 sleepers restored for posterity, and indeed the same for Mk3s. I would donate to such a project, but of course for the reasons you say it's not the highest priority.
There is a separate thread on surviving Mark 1 and older sleeping cars at www.railforums.co.uk/threads/surviving-pre-mark-3-sleeping-cars.168771/