Irrelevant characters should be eliminated during the edit of the script (or any kind of story), but I admit Maul served his purpose. It had more to do with wowing the audience than advancing the plot, I fear. Until he killed Qui-Gonn, I didn't really care about him one way or the other, which should be an important point. It would have been more interesting if Dooku had done it, but that would take the story off in a different direction...we'll never know if that would have been a good or bad thing.
You shouldn't HAVE to learn more about the characters in the movie by looking beyond the movie; it should be IN the movie. That being said, now I know Binks' purpose in the grand plan, I understand why we had to put up with him in ep1. And the whole purpose of the prequels is to see Anakin on the road to Vader, so the movies do succeed with that. It's a shame to see them let down by the other stuff, is all.