When we say prominent here, we don't mean "face on a billboard" prominent. Rather, these are characters who are absolutely secondary to the action of Adam Bede, but who each get their proverbial fifteen minutes of fame. Old Martin, for instance, gets to hold open a gate while his family walks to church, "pleased to do this bit of work" (18.9). And Wiry Ben has a chance to show off his dancing skills at Arthur's birthday, "with graceful turns of the haunch and insinuating movements of the head" (25.45).
Why are these descriptions in here, though? First, because they're funny. Second, because Eliot's realism is all about slowing down, savoring the world around you. Eliot's narrator looks back fondly on the old days when people had fewer "doubts and qualms and lofty aspirations" (53.55). Life was calmer and more considerate then. So let's all slow down and watch Wiry Ben dance. Maybe Adam Bede can teach us all how to take it easy again and give everyone a bit of attention.