Do the OEM mudflaps actually help to keep the car clean? One thing I have noticed is that the Golf seems to get dirty much quicker than my CC
They may stop mud being sprayed up on the sills and lower doors and help reduce the risk of stone chips on the lower side panels, but IMO they won't do too much to stop the car getting dirty from general road spray from wet roads or salted / gritted roads..
I had mud flaps on my mk6 GTD and at this time of year, it got covered in just as much road salt as my current car (Polo GTI) with no mud flaps (VW don't make mud flaps for the Polo GTI anyway, so I couldn't have them even if I wanted them, but not really missing them).
Because of the shape of modern hatchback cars, rear mud flaps will do little, if anything, to stop the rear of the car getting dirty. Movement of any Golf-shaped hatchback car through the air will still result in road spray getting sucked back onto the tailgate and rear window, whether it has mud flaps fitted or not.