I would advice you to get on
www.ebay.com and search for old(er) books; I myself have found some fine hauls there.
Then, from my own experience, I don't think that the way of interpreting the cards has changed dramatically since the beginning of the century. Perhaps, as with modern astrology, has it become a bit overly influenced by psychology, but in the end it really just comes down to your own abilities and how you choose to read the cards.