I'm twisted with that sealed stuff.
If it comes for consoles, I can't understand why anyone would keep them sealed. There's nothing better than open a new package and peal of the plastic film (slowly, very very slowly). But I don't think about selling them anyway.
If it comes to games or special editions: well, I open them if I want to keep them. I can't imagine anything more boring than having a sealed box on the shelf without ever knowing how the stuff inside really looks.
I have two sealed CEs right now (Zelda) because I don't plan to play them anytime. I have a sealed Bayonetta because I don't had the time to open it. The same with some games. I open them when I want to play them so they are sealed right now. But I would never ever pay a huge amount of money only to own a box where the only time I see the content is on the picture on the outside of the box
Just my opinion.