mjh: For personally I can see noticeable weight differences, being bogged down with Quattro, but for the higher Golf models the weight reductions of "up to 100kg" has resulted in about 30kg reduction over the old Golf. My manual 170TDI Scirocco is only 18kg heavier than the manual MK7 GTD. I doubt i'll even notice it.
For company car drivers where BIK is critical, stick with the GTD
For people that like diesel delivery (and economy), stick with the GTD
For private buyers still wavering and waiting for a UK demonstrator, I give you the Seat Leon FR 1.8 180PS, £18.500 with tech pack amongst the many alternatives.
It might be possible to notice the 70Kg weight saving.