KiCad simply was not ready back then. It had many missing features. (Including lots of stuff that would make it possible to reuse the project.)
See the early versions as beta releases and everything makes sense.
Oh and i have to disagree with the project is lost. I could open it normally in version 4. As expected the missing cache library made sure the schematic is basically a lost cause (This is the fault of the original designer. One can not expect the software to work if you do not include all the data required.)
The only thing that is a bit lost are copper zones. But they are rebuild easily. (This is because copper zones where bodged in the first release. If you look at the file you will discover that kicad simply put a ton of traces to fill the area of the zone. There is not really any info about the zone itself only the traces.)
As a note: one can view the project in v4 without fully loosing the zones. (But the zone looks strange. -> missing the outermost outline, only the traces for filling are shown.)
Oh and regarding your bomber: Well yes the documentation for it still exists. So you can maintain that thing and if needed even build new parts for it. (For the later you might still need to draw that part new in a modern cad program if you want to use modern manufacturing technologies like CNC.)
If you would want to make a medium modification to it you would basically need to start from scratch as the design files are not available in a digital form.
Same here. Making the same unmodified thing is easy as the gerbers are still valid. Modifying it is possible if the original project was created and archived correctly. (including the cache library would be the minimum requirement.)