Yes, I know the feeling well. Not only do I have duplicate papers and embellies, but books too! At least they were only thin paperback books--more like booklets--instead of expensive hardbacks. I have resorted to inventorying all my scrappy stuff and do not put a new purchase away before getting it on the list. That has helped tremendously.
Not necessarily with paper, but my daughter jokes that her scrap room is well-stocked with my duplicate purchases! Even with my very detailed index book, I still find myself falling in love with something when I'm without my book, getting it home, and when I go to enter it into my book, discover it's already there!