I had stopped watching the show around the time of the David & Hallie/Gerard & Daphne story (my mom put me in some after-school program from the fall of 1970 onward, so I lost touch with DS from that point on). Months later, when I heard the series had ended recently - I was back east visiting the old neighborhood during Easter in '71 - I remember how devastated some of the kids were: suddenly it was 4pm on a Monday, and they were at a total loss. Sure they could play on the swings or go buy some candy at the corner store, but for the last 3-4 years, they'd been sitting faithfully in front of that TV set every weekday afternoon, tuned in to ABC, waiting for Barnabas to swoop along.
There was another short-lived soap or two I had followed prior to DS' departure ("The Best Of Everything", also on ABC, and "Hidden Faces" - I think on NBC), so that softened the blow about Dark Shadows: I was already seasoned at saying goodbye to axed daytime stories I'd been watching by age 8!