I guess the sound thing is a subjective thing. As long as it's as good as better than the Delta and DSP in my current Passat, that'll do. I mostly listen to Radio 2 and a cd when Steve Wright is on. I can't imagine the difference being between night and day to me to me, so maybe the 510 will be fine.
As for the rear camara, I know I have only used it once, but I found myself with my head down and concentrating on the screen, which meant I wasn't paying attention to what was going on at the front of the car like I would have been if I was using the mirrors. It was a bit like when you see women reversing looking only over their right shoulder without a thought to where the n/s front is.