It really is a waste. I had received some MS points as a gift so I used them to unlock some decks but it really is more enjoyable to unlock them by winning. In my defense, winning is now much EASIER with my unlocked deck. Winning in campain mode, that
is, I stink when I play live, but I'm learning.
It *IS* a total waste. The cards you see the computer using are only in challenges. Any cards unlocked with deck keys can be unlocked by winning matches... FOR FREE! There is nothing exclusive when you buy a foil deck.