Everywhere is a source of inspiration. Your friends, your neighbours, your enemies. For writers you can take revenge by making your enemies villains in your stories. (Muah ha ha ha ha... It's true. I just read that the recently deceased Ingmar Bergman created a character based on his father whom he didn't like).
It gives you more motivation to find out about people. What makes them tick. It does in fact, make people more interesting.
Now that I'm writing, people get more interesting. You want to know their background, the parents, their friends, their aspirations, their fears. Not that I want to use people as source material, but rather that you realize that everyone is unique and has something interesting about them.
Everyone has their own story to tell. Some may be in Act 2 of their careers, Act 1 of their marriage, Act 3 of their relationships.