Well if you have a grand to spend, then turbo back exhaust and re-map, maybe a bit of money spent on the induction if you've got any money left over.
Tunning diesel moves the torque higher up and defeats the object of owning one. Also I think the Golf cannot put the power down very well and the clutch struggles
If your clutch is struggling then get the re-mapper to wind back the low rpm torque to a more acceptable level. I had to do that on my 140.
I can't see how moving the torque up the rev band on the Diesel defeats the object of a Diesel, you don't drive everywhere at a steady 1900rpm do you? Remapping it gives you a broader more useable torque band that allows you to use the higher gears (thus lower rpms) and the fuel economy stays at similar levels overall. I have pushed this boundary somewhat on a couple of my cars, but hey ho, all in the name of science!

Anyway the added fun of the torque surge makes it worth a few lost MPGs anyway.
My remapped 140 did low 40s mpg where I doubt you'd get near 30mpg in a 2.0tfsi petrol unless you've got a brick under your accelerator pedal.