Interesting topic. Unlike many fans, I've never felt the impulse to own Josette's music box, Barnabas' ring or his cane, though the latter is VERY cool and magickal.
What I did crave and demanded until my own set was given to me were Magda's tarot cards (I didn't realize that they were originally owned by the Countess du Pres until many years after the run of the original broadcast). I went to the library, checked out Eden Gray's tarot books, and made my own traced copies of the major arcana cards until I got my own deck as a Christmas present in 1970. The deck I was given was the "IJJ" Swiss one (so called because of the Jupiter and Juno cards that are said to be unique to this deck), which was the same one used by Magda. Back in the Sixties, it was still very difficult to find tarot cards. I really wanted a Pamela Colman Smith (aka "Rider Waite") deck because I loved the images so much, but had to wait until just a few years ago when I finally bought one for myself.
Other props I loved on the show were the painted Egyptian-looking coffer that held Count Petofi's hand (and was often glimpsed on an end table in the upstairs corridor in the present-day episodes), the Naga box, Laura's scarab, and, of course ... THE AFGHAN!!!
Does Cassandra Collins' wig collection count as a prop? That would be on my list, too.
Gothick