I think there is a kind of ranking of rareness - and it depends on the type of collection you have. For me, at the top, there are the irreplaceable historic ones - whether or not you'd use your Pam A or 19th Century Gumppenberg. Then there are the rare decks that we really think are not going to be reissued - like the Ironwing or Greenwood or Bohemian Gothic Silver - then there are the ones we think of as rare because they are OOP and we have seen prices creep up - someone mentioned the Rumi, but there's also the Royal Fez Moroccan, Lisa Hunt's Fairy Tale, Fantastic Menagerie etc. This last list is, naturally, the longest.
I've been in tarot long enough to see the desirable OOP ones that people paid good money for come back into print - the Alchemical, Hermetic etc etc, so really, if it's a mass market, mainstream publisher, it'll come back into print at some time. I always think like that - so like, you don't use a deck you love for twenty years and then it comes back into print?
I know the idea of back ups is not for everyone, but it definitely changes how I see a deck - I make fewer impulsive purchases from LoS and Llewellyn and US Games and then buy extra copies of what I like when I see it reasonably priced on ebay or here. I have two BG Silvers, three Greenwoods, five Royal few Moroccans, three Hunt Fairy Tale tarots and various others. These are decks I love and I now use without a second thought.
But I think it's wise to be careful - hoard for years and then watch it come out mass market again? Not a great feeling...
Historic ones I tend not to use regularly - just gently and for me. If a deck is really fragile - not relevant here but like my Destroyed Dondorf - it is in plastic sleeves and I use Tag's reprint. But I do use my Pam B. Cards don't deteriorate. The worst that can happen is you either lose a card (so be attentive!) or you bend when shuffling, but of course you shuffle more carefully. Plus I'm not getting any younger. Two more decades left? Possibly. How many decks can you grind to a fine powder through shuffling in two decades?