Or replace the car radios buttons by a steering wheel? Oh, did someone say iDrive?

I basically agree with you. But this imho still doesn't need a completely different UI. Some basic new widgets may be sufficient and these could even be used by other applications in turn.

E.g. the application installer introduced the hildon-breadcrumb-trail widget (the navigation bar on top). I really enjoyed re-using this in gpxview and since most users have used the application installer before they were familar with this kind of bar in my program.