Trust me, the boxes greatly increase the gun's value.
It can take a "400" dollar gun and bump it up to a "450 or 500" dollar gun... Aslong as the original box is in good condition.
As for chairsofting... Guns that I own that are not for sale:
1X PDI VSR-10 1X TM MEU
Even when I'm going full out I limit myself to 1X Sniper 1X Pistol 1X Outdoor/Indoor gun