I always wonder if the Hastings/Denniston relationship ever got tongues wagging as the '70s articles about Don always give the happy home life impression.
I've never seen Karen - I wish I could (again mostly just to see Nancy's reaction to her).
You probably already know this but the 79/80 ATWT clips on Youtube do start the building of Dee's relationship with her ex. (Ian?) It makes sense that such a terrible experience would make Dee vulnerable to John's manipulations, but it all feels very crass, as Dobson material from ATWT tends to feel.
The Holloways were just a bust (and making Miranda into such a blatant Iris replacement did her no favors, since, as you said, the show had moved on from that type of palate). Of the family, Hobart's character was probably the best for me, as her little story of falling in love with do-gooder Jerry in spite of herself could be touching at times, but even that wasn't really worth the time. I most remember that era because they had 2 or 3 men tooling around the family at the same time who all looked and talked alike. Baffling.