I thought some of it was bad casting until I saw the press announcement
http://youtube.com/watch?v=sznsg7hRD3U

The whole cast is perfect if you take Speed Racer and turn them all into Americans. Speed Racer was so long ago, it's hard to even think of it as anime. Emile Hersh is perfect for the goofy way the Speed was always portrayed in the American dub. This was back when they renamed every character, took huge allowances with the translation (if they bothered at all), and generally just made the series completely different.

The Wachowski's are big fans of anime. They're paying tribute to the shitty dubbed version they were presented with. It's a great way to make a really cheesy family film.