Like opb I've enjoyed the idea of creating a fictional universe in which characters reappear in different stories. I learned this from favourite author Kurt Vonnegut who did the same thing (notably in his 50th birthday present to himself "Breakfast of Champions"). One character who crops up in different Vonnegut novels and stories is his science fiction writer Kilgore Trout (perhaps based on Theodore Sturgeon), author of the ingenious "2BR02B".
I wrote "Cropton Girls Play Spanking Cheat" partly out of a lack of inspiration for creating new characters, and partly because the idea of 4 women playing the card game "Cheat" with plenty of spanking sanctions was a fantasy that appealed.
I also have a Jessica who stars in "Seat-Warmers Unlimited", "She's for the Cane" and "Padded Seats in First Class" in her role as a spanko journalist, reappearances which happened mainly by accident.
I have yet to try writing non-spanking fiction, but when I do I can imagine borrowing characters from my existing fictional universe.
In a sense, every character we create is a part of ourselves; some demand more air time than others and are more of a pleasure and adventure to build fictions around. Using them to dissolve writer's block is a good idea.