essentially, we've done exactly that. Now have a mark5 gti and as u say it does everything, its easier to mod than the r32 at least in terms of output, and the Mark6 is in our view better looking, but an expensive car f u then want to add mods etc. The R32 we had was DSG and to us, a bit boring. Mark6 gti was uber cool (white, 3door, 18" monzas), and sold in a moment of madness for a 2006 RS4 avant.
cheers,
N&J.