Aren't there some products who's value increases when you open them? No, wait, I think it isn't the actual value. Maybe it's the desirability? I have no idea where I heard this, probably Pawn Stars or something, but with something that normally has visual appeal, but is hidden in packaging, I think opening them is actually for the better value-wise. Not sure, though. I'd open them, personally.
Lol - first love Pawn Stars but half the time I am pretty convinced they make things up as they go along
Second - I actually think you [or they for a change] are right! Its not so much increases value as increases desirability. I think you see this with some ponies - I am a loose and complete collector but for some ponies I find it easier to track down and pay for MIB ponies than loose and complete versions. My MIB Princess Moondust cost less than the complete [with all her accessories] version! But this is really only limited to a few ponies and only if you have the right collectors interested.