My experience, though coming from a different place demographically, was like Steve's. When we turned on TV we watched the shows we watched and saw the actors we saw without knowing there was any back story. And nobody in my parents' generation mentioned the casting, neither approving nor condemning it.
I watched Star Trek in the post-school slot as a M-F daily syndicated show. I just don't remember any feedback in those days before the conventions and cast autobiographies. Nobody asked how a Black woman could become a Starfleet officer or why she was just the receptionist. I don't remember seeing or hearing any reaction to the interracial kiss until decades later.
And as for Linc being a Black character white audiences would like to watch, well yeah. CWIII, Lawrence Hilton-Jacobs, Jimmie Walker, Don Mitchell (I had to look up the Ironside cast), Greg Collier, Diahann Carroll, Nichelle Nichols, etc all had to play characters who appealed to white audiences or southern TV affiliates would have pulled the shows from their schedules and put the networks on the defensive. In 1979 CBS put The Dukes of Hazzard on the air with all of its confederate imagery and got no pushback.