I do wonder whether the camera makes you focus purely on the car behind you more than the overall position of your car in a space e.g the car is 12mm off the car behind it, but is in it's space at a 15 degree angle.
Never been let down by the rear sensors on my Scirocco yet - they pick-up bollards etc with ease. I'd consider the camera and park assist (and any other driver aid) as gimmicks if they don't make the task they're assigned considerably easier, and parking a Golf is already a piece of cake with it's great rear visibility (much better than my Scirocco) and parking sensors all around. If you think you might want or need them, they're 2 of the cheapest options you can get, so relatively speaking it's not much to shell oout for. I'd be far more tempted for the camera if it activated for 5 mins recorded time when the car was nudged (to capture hit and run drivers in the car parks).