This is a really interesting discussion, not something I had thought about before. I'm not much of a collector, but my view is from a performing point of view - I like interesting or unusual decks because of the colour they add to a performance, so from that perspective, obviously I'm going to open the cards.
From a creators point of view, the few decks I've designed have been very specific - the first was for use on a TV special, so in my mind it was a prop and obviously to be used - they weren't supplied shrink wrapped so opening them was a no-brainer. The new deck was less focussed just on just one performer's presentation and meant to be more general, for everyone, but again very focussed on performance for both magicians and cardists, as well as some custom art for people who like that sort of thing - they are designed to be used.
I guess my approach is that the style of the cards is like the cut of the suit you wear, the fashion of your clothes. Not using the deck, even for your own amusement, is like buying the suit then leaving it in the wardrobe. BUT: that analogy works both ways - a friend of mine managed to acquire one of the nazi uniforms from Indiana Jones and he definitely DID keep that in the wardrobe with a view to selling it for a tidy sum rather than wearing it out and about. Some things you buy to use, and some things I guess their value as part of your collection is greater than the value you would get from cracking it open for a shuffle.
Thanks for the various perspectives.