I don't think you could say it's overkill or not simply based on the idea that you're developing an indie game. IMHO The guide for this sort of thing is always what you're trying to accomplish. It's the program itself. It might be overkill if I could say for instance that a game engine doesn't really require this kind of plug n play interface. Or maybe it does. It really comes down to why you're using the pattern.
Some people use design patterns and UML etc...for the sake of using them or because they just read a book on the subject. Other better developers will happen apon a design pattern and not know it because it happened to be the solution that fit what they were doing.
Being familiar with design patterns is not a bad thing. There are common one's because to some extent the same problems need to be solved often and the same kinds of solutions are useful. But IMO your goal as a developer should always be to make the simplest nicest interface you can. Sometimes that's a design pattern and sometimes it's a trick using the c++ preprocessor.