Actually, in a sense, I think a good fit is crucial, because it addresses one of the complaints that people usually have. You can't really get away from helmet hair or the heat retention of poorly-ventilated designs (like my helmet I mentioned in my first post), but anything that makes it fit more comfortably will also encourage the rider to wear it more.

And, whether someone believes in the effectiveness of helmets or not, they'll agree that, if they wear it more, they'll get their money's worth.