I’ve certainly got enough mileage out of it. I focused so strongly on lesser (or original/outsider) characters in the beginning of my fanfic career, for the first several years the joke with my kids was that I was a Buffy writer who never actually featured Buffy. Even now, there’s almost always some non-core character who reacts to the mains and/or has them react to him/her. It’s just effective as well as fun.