Eh, not really. Unless they have info on a feature that was removed. Most of the time, prototype manuals are interesting but not practical, since it basically means "preliminary".
For practical purposes, it's better to have the latest version of a manual, the schematics, or any other relevant paperwork.
Later versions usually have corrections and updates prior versions might not have. Prior versions may have errors or omissions.
But in cases where there are details for a missing or prototype feature that was later removed, I suppose it could have some value to prototype game owners. It just probably won't be worth a large fortune since most things have been scanned and are available as PDFs at this point.
Long story short short, it's probably worth about the same as any other manual in nice condition.