And, like it or not, any altering of the original confguratin will affect the value.
Example. I have an Osborne 1, tan case, which I have altered with a non-Osborne floppy controller which allows for 3.5" drives and up to 4 separate drives. I've installed a 3.5" and 2 5.25" drives then I added a 150W power supply. The unit is much more usable, but from a collectable stand point it greatly reduced the value of the unit.
If I had used the Osborne double-density board I would have maintained the value of the unit but reduced the usability of the unit. Since it was my primary computer at the time I made the choice to go for functionality.
Still it is his choice.
Curtis