Great topic!
I'm an avid collector of DS and classic horror film memorabilia. Sometime I'll have to post a pic of my "Forry Ackerman" basement ,[frankie]
I painted the walls stone grey to resemble the Old House basement.
DS wise, my most "valuable" items would probably be
1.) The cards-I have a complete set of the original pink cards, the green cards, the recent orange cards, and the color photo cards, although I lack the signed Dan Curtis card, I do have the signed Selby, KLS, and Roger Davis cards.
2.) I have about a 1/3 of the Gold Key Dark Shadows comics, including a # 1.
3.) My wife has a complete set of the old paperbacks, including the cookbook and all the novels.
4.) I have the original one sheet (standard theatre size)
posters for HODS and NODS, (style 1 on each). I paid about $75 for HODS about 10 years ago and I've seen it go up a lot since then. I have the complete lobby card set for HODS and most for NODS. I hope to complete that set one day.
5.) Most valubale to me personally is a 1968 cast photo, the one they are standing on the stairs in, signed by John Karlen, KLS, Nancy Barrett, Lara Parker, Jonathan Frid and Louis. (Bless his soul). I wouldn't part with it for anything, although I'd keep missing Robert Rodan at shows and wish i could get him to sign it as well.
Sincerely, no bragging, I'm just proud of what I've collected.
PS One day, I plan on adding a skeleton in Trask like clothes in a unused closet, and put something that resemebles a partially bricked up wall in front.