Personally, I absolutely love old books, partly because I've got a collector's mentality, and I'd rather spend a ridiculous amount of money on a beautiful hardback first edition of something than download a PDF or get a modern paperback. However, if you're looking at it from a practical point of view, and you're just about what you can learn from it, I'd still say old books (reprints or otherwise) are incredibly valuable.
Firstly, there is nothing ever invented completely in a vacuum, all modern moves and routines stem from older influences. However, these new inventions are simply the result of one person's creativity when presented with the source material. You may very well see subtle elements in the original that haven't been used in the updated versions, and thus be able to innovate for yourself.
Secondly, have you seen how much magic literature there is? Even if you confined yourself to the task of studying only Marlo's work, you could spend the rest of your life mastering it. Apparently even he couldn't do it all, a lot of things were just ideas that he was thinking about but never got down to practicing seriously. This means that there are definitely a lot of moves and routines that modern magicians haven't got around to updating. The mine is by no means exhausted. The Bucks, Lee Asher, or whoever your favourite card magician may be, may have read a lot of old texts, but I can say with certainty they haven't studied everything. Therefore, there is nothing stopping you from finding those hidden gems and fooling a whole new generation with them.