Meh, quality of the Mk5 is way above the Mk6.
Mk5 doors - 50 man-hours to build.
Mk6 doors - 10 man-hours to build.
Mk6 is meant to "feel" more expensive - there's that industry thing they call "percieved quality" (as opposed to, well, actual quality). In reality it's cheaper for VW to build. Early Mk5 GTI/R32 was the high-water mark for the Golf IMO.
But then I'd say that.
Rather than splash out £30k on a new car why not drop half that into your current Golf? If you're after individuality then that would be over and beyond throwing some graphics and paint at Mk6 R.