What does the MOT cert say?...if it is just "advisory" don't bother replacing until you get a Fail on them.
I had my car in for MOT & I said I'd get an advisory, & the MOT did come back with that & a price for the job, which I refused as not a "Fail".
Rears on the MK7 Golf are way over braked for what they do, so they will never get shiny & I have always had rears on my cars get scored & rusty....fronts is a different matter...fronts on the MK7 are underbraked...IMHO...
If you want to get new discs & pads get a set of plain ATE discs as these are made to very tight tolerances..& get their low dust ceramic?? pads...I have their grooved discs which work with their plain pads on the front..
PS I'm near to you & have legit VCDS if you need some work doing..