I have all my Canon gear boxes, camera body, lenses, converters, extension tubes etc. And I am actually thinking of selling a couple lenses so.. I am hoping that a neat tidy package like you'd get at the store will be more appealing to a buyer, it is to me. It's not like I will charge fifty bucks more for a box particularly since there's nothing vintage going on however I would think presented properly with all the packing, manuals etc in tact as well as gear that's been taken care of would warrant a better price than something displayed with an inch of dust on it, no caps, no box, etc.
As to buying, if I am collecting I try to get the best package, box and all but not at a ludicrous price, because yes, to me, most times these items seem to be better taken care of than ones missing all of that. What I buy, even when old, is new to me and it's fun to get new things that actually look like new things even when I intend to use them. I;ve gotten a couple Konica lenses like that, appear new, might even be since they were in the boxes, plastic and all.