What are so special about these two computers? (Special enough to go through the work of making clear cases for them).
The cost of the new cases exceed the value of the Macs themselves, so what is going on here?
Those computers in itself are today, compared with what current computers can do, absolutely nothing special.
But, what you do on a computer today, has been largely a result of how those old computers were designed.
They are essentially pieces of history, hugely important steps on the way to how we "compute" today, if those computers would not have existed, or when back then they would have decided on other directions, the way you today would use a computer would also be totally different!
So, that is part one, they are part of history.
Second part, obviously they were not designed to be working 40 years after they came out of the factory.
The parts which are used in them over the decades deteriorate, to the point where they do not work anymore.
Especially the SE/30 (and lots of others from that time) used capacitors in metal housings, essentially little batteries, which start to leak decades after they were manufactured. They leak acid, so after a while those machines simply become damaged beyond the point where you could repair them.
You find one which has been stored away in an attic when working, 10 years ago, take them out of storage today, and they'd be damaged beyond repair.
Which means, every year less and less surviving, working machines are left on this planet.
Which is the reason people spend time and money to restore them before they get to that point of never being able to be repaired.
Just to preserve history, and that is where that clear case comes into play, it's a showcase of history, putting the last of those working machines into a display to show the next generations how current computers actually came about!
Actual working and restored SE/30's can fetch several hundreds of dollars!
Go back just a little further to the Apple Lisa (which is basically one of the first commercially available computers with "windows" and operated with a mouse, much like we still do today), and you are talking a few thousends of dollars/Euro's for a Lisa 2, or tens of thousands for a Lisa 1.
More in the line of the Apple II, the predecessor of that one, the Apple I, original and working, you are talking hundreds of thousands of dollars!
So yes, computer history is both important and valuable, so why not splurge on a clear case?