In an unscrupulous dealers hands, these boxes do have the power to transform a used gun into a LNIB gun, but the price differential is often similar to the price for the boxes. I'm not sure what is going on here.
In the past, I have used blue plastic Colt boxes to carry trade fodder at gun shows. When cruising a show with such a box, I never fail to get immediate attention if I belly up to a dealer's table to take a look at his guns. I never have to wait if I have a Colt box. Invariably I am asked "Whatcha got in the box?"
"Just an old gun," I reply. I usually have an old beater H&R revolver and a few grips to trade off in my Colt box, but I only open it when I'm ready. Even then, I am often offered cash for the box. Right now, I have seven or eight blue plastic Colt boxes in my gun room. Perhaps I should ebay them and get myself another gun......