I did this to my old 1.9 TDI 130 and it did make a good difference, mine had the same 288mm setup as used on the 1.8T.
As above, you'll need caliper carriers from an S3 to get the 312mm setup on - I got mine from a forum member for about £50
I'm not sure if the other diesels such as the 110TDI use the same setup though.