I'd argue that point a bit.

While there is ton of it, for people looking at the history of how these games were made, this sort of stuff is a treasure trove. Having said that, at the current point in time, there are almost no true historians for that sort of thing - and maybe there never will be. If that is the case, they probably aren't overly collectible and aren't worth much beyond a cool conversation piece for a lot of people. If, however, a historical value is found in them at a later point, the price to return even a fraction of the drawings will be significantly higher, which would increase their value significantly and raise their collectively.

The thing is it's rare that we know what is going to be collectible at any given point in time. When I first started picking up pinball machines, people were certain that they wouldn't be worth much in the future because no one was ever going to get parts to fix those machines when they broke, so the belief was we'd just end up with less and less machines becoming less and less valuable as their working parts dried up. A change to the market - the introduction of repro parts - played a huge role in turning that around and making things more valuable.

While it's less likely, an increase in the curiosity of the history of pinball could easily make these nearly priceless. It would take one or two people with really deep pockets instead of a larger movement, however. Until them, they are fascinating.

I own a set of blueprints for Galaxian that I bought a number of years ago. I don't know where they are now, but I do know that I looked through them for a while and found them fascinating as I really like that game's history. Those are mostly diagrams of screws and cabinet joints though, so I don't anticipate them becoming suddenly super valuable, but they are neat to me. For anyone looking, I would suggest the same thing. The price they go for now is probably about the price they'll remain worth for a long time. Chances are they are one of a kind now because this would be from the archives, and would be what was kept as a "just in case".