As long-term readers of my blog may know, I used to take a rather dim view about the use of playing cards as instruments of divination. Recently, my attitude towards this has softened.
The fact that tarot was invented as a means of amusement, this does not mean it is an an illegitimate method of divination. People have been divining using all sorts of things- thunder, stars, animal entrails, coins, the output of random number generators, etc. One can hardly say the stars were invented for the purposes of divination, but yet many people use them as such, and indeed, if we believe them, gain great meaning from doing so.
In turn, the divinatory use of playing cards - tarot or piquet decks- is one use amongst the many uses of playing cards. Collectors of playing cards would impovrish their collections, and indeed, their knowledge of playing cards if they ignore these divinatory uses.
Further, these divinatory meanings traced in their instruments. Consider tarot. Cards are interpreted differently, depending if they are upright or reversed. As such, this means all modern divinatory tarot decks are produced in such a manner that they are single-faced. In turn, many of the tarot pips are made in what are other contexts called 'transformation' cards; the particular figures on each card corresponding to the card's divinatory meaning
Thus, just as much as collectors of playing cards should be aware of the games that these cards are used to play, they also ought to pay attention to the manner in which the cards are used for divination.