I'm a little late gettting in on this because we've been away.
While they remain secondary, I love writing about the secondary characters because we really don't know much about them. That gives a writer a lot of room to play. Making them real and human is always a challenge, too. I also love creating new characters, especailly villains.
My favorite secpmdary canon characters are Henderson and the original Jimmy. I could never forgive the new Jimmy for saying, " Lois isn't here. Her and Clark are out on assignmnent."
Jude