Halloween diecuts and paper decorations are generally more rare than plastic items because they are so fragile, and because they were inexpensive. Collecting them is a really exciting hobby though, and there is a lot to learn, especially before going out and actively seeking out pieces.
Some are truly old, but aren’t at all rare. I’ve gotten loads of old Halloween diecuts for free or very, very cheap.
There are many good books out there, but my personal favorite has got to be Vintage Halloween Collectibles: An Identification & Price Guide by Mark Ledenbach. It is full of helpful information and eye candy, too.