Considering the spec on your car already, whats £165? This is an option which was on the top of my list.
I don't like sensors as I have backed a car into a tiny brick wall. Sensors were still bleeping as if to say's the room but it couldn't detect the low down object. By having the camera to reverse, I have the piece of mind.
Park assist is a bit of a gimmick IMO. Since driving, I've probably only parallel parked once. If I was doing this day to day, I might look at it, but I don't need it. And I like reversing into a spot dead quick and perfectly in the lines when you see people giving it about 5 attempts.
And FYI regarding the dealer. Just tell him to add it on. Say you've got a buddy who works for VW and says the option is back on. If that doesn't work, use the below and tell him to get his manager to check their VW logon.

