I wanted to point out the usefulness of eccentric characters for comic relief.
In a lot of serious stories there are high stakes and without a little humor to break the tone of constant running and fear, the story will become tedious and the reader may lose interest. By using an eccentric side character to break up the tone, you can inject some humor and make a lasting impression on readers.
From my own experience in short filmmaking, I notice that it's the films that make people laugh that are the ones most talked about. People like to be entertained and watch someone wacky either make a fool of themselves, make fun of the main characters and their attitudes of seriousness, or save the day. These are all great things that you can have a side character do, all while moving the plot forward and making your readers chuckle (hopefully).
Don't be afraid of going over the top. You can always dial it back in the second draft.
My latest comic relief character fascination: Frances Conroy in the third season of American Horror Story. Definitely check it out if you haven't had the chance yet! She's a riot.