Thank you John for the printing information.
As for options: Personally I prefer a hardcopy version to read and look at rather than a CD or ebook or whatever. If an updated new edition including all the old content was produced I would certainly buy it at £60 or so and would regard it as a bargain given the cost of modern academic texts. I think I would buy two. I would also buy another copy of the first edition, as is.
If a supplement was produced: 'A supplement to an encyclopedia of Spring Air Pistols, Vol. 1' then I would also buy it, again most likely two copies.
Note: the Vol 1 is not obligatory
Cheers, Phil