They should be played at least to get a good transcription onto other media, otherwise what's the point?

I would play it, but I would probably drop it too!

To me this is a historical document and I'd no more play it than I'd take an original copy of the Magna Carta or the United States Declaration of Independence to bed for a bit of a read. There are perfectly acceptable (and in fact more readable or, in the case of the acetate I'd guess, more listenable) copies of all of them if I feel the need to get up close and personal with a bit of history. Don't forget, also, that this is an acetate and so will degrade much more than a typical vinyl release from playing it. Finally depending on your stylus tip profile/tracking weight combination it's possible that you could damage the actual layer of acetate irreparably.

I can't give a definitive answer on that one, but I'd bet it was.  I'm pretty sure they never recorded so much as a sneeze without it having found its way on to a release of some kind, somewhere, by now.

So really a collector's item only if not unique

Since it was sent to George Martin as a promotional disc, it has already been played so is no longer mint or unplayed. Despite the fact it is a 78 acetate and therefore fragile, it can still be copied virtually without damage if the necessary care is taken. Record libraries do this all the time.

The comparison with written documents such as the Magna Carta is spurious - they can be read by the human eye and reading them does no damage (provided the ambient light levels are not excessive), so provided no errors are made in the actual transcription, the copy is as good as the original. A record on the other hand can only be read by physical contact with it, and therefore in doing so can wear.

But since these acetates are going to be bought by someone as a speculative investment, they will languish in a bank vault just as they did in the loft. Perhaps of some interest to historians of mid-twentieth century pop music, I can't imagine they would be of much interest to the majority of music lovers. Now if it had been a recording of Robert Johnson's mythical 40th song ....?

As an aside, the longevity and usefulness to archiving of recording tape (and of optical storage) has been called into question. It's quite possible that in 100 years time, all tape will have degraded as well as optical storage, so the only hard copies will be the vinyl in record collectors libraries! Makes you think.

The last I heard was the laser was so sensitive the records had to be scrupulously clean, otherwise the laser would read the 'dirt and dust'. I think there were also problems with keeping the laser focused whilst tracking warps.

Whatever, the Finial record player died a death; possibly because it was introduced at the same time as people were ditching their vinyl in favour of CDs.

I agree about not wanting to mistreat either. The question is is the replay of the 78 acetate by careful means in order to copy it actually mistreating it? Is it better not to know what's on it and await for such a time when a contactless means of playing it is developed, or to play/copy it now and risk the, albeit slight, wear of the sick that would entail?

Also agree with your comments about the re-think on the use of 'white cotton gloves'. The argument is that without gloves there is better bio-feedback when turning a page - the page is turned more gently and less stress is put on it. First time I saw this on TV I was taken aback, but discussing this with someone who works at the National Library of Wales, I was told of the new thinking on handling old and valuable archived documents.