When I watched DS back in the 60's and early 70's, I was also watching other soaps--AMC, The Doctors, GH, Ryan's Hope--all of which celebrated holidays up the ying yang. By the time DS came on, I was actually relieved to see a show that bypassed the Christmas trees, Irish merriment and Thanksgiving celebrations. With DS standing by itself now, I guess the lack of holiday celebration is more glaring, but I didn't really miss it.
To me, DS was almost a parallel universe unto itself. They never mentioned the Vietnam war or any other historically-related events (although I think they DID mention the moon landing). When they did bring up references like that, or rare holiday mentions, it seemed to bring in a whiff of reality that seemed out of place--IMHO, anyway.
Granted, I can see some poignant scenes featuring the Collins family, (happy, just for one day!) around a huge Christmas tree, Barnabas and Roger as excited about opening their gifts as David and Amy.
DARK SHADOWS was rushed from one cliffhanger to another towards the end of the series, to its detriment, some believe. Remember, though, it was very much aimed at children, and children, like Dan Curtis, have a short attention span. He was forcing his writers to produce scripts targeted at that audience.
Love, Robin
PS - Merry Christmas, Happy New Year, Halloween, and every other holiday to the Collins family!