I've got an older one.
The sound is a *little* better without the waterproof case, but not much.
That said, there's other uses that you haven't thought of:
Diagnosing suspension noises and stuff is MUCH easier with a camera. Not that I've fixed any of my squeaks and creaks, but now I know what I need to do to get rid of them.
Timelapse with it is really easy, and cool.