Sootchucker: It's always a bit of a lottery when keeping a car out of warranty, but VWs seem to be at their least reliable when under warranty. Apart from suspension issues as the car ages, things seem to fail on VWs early on, most likely from manufacturing defects on the parts that wasn't apparent at the time of build. With all the issues i've had on 7 VWs prior to the R, they've always happened within the first year of ownership.
My had has ran 2 performance TDI Golfs for a lot of miles without issue and they were both DSGs.
One was a Maltese import MK4 GT 1.9TDI 130 DSG from Carshock, ran for 130k miles.
The other was his last car, a MK5 GT 170TDI, ran for 123k miles, around 70k miles of it with a TDI-Tuning box. Neither car missed a beat, the MK5 had a recall on the injectors, they were replaced at 110k miles at no cost and the car saw an improvement in running.
I paid for the 5 year warranty on my R - as much for making it a more attractive proposition on a private sale if I chopped it in at 2 or 3 years old as it was for the reassurance should I keep it that long.
IMO, you shouldn't chop in your GTD for another. The GTI is marginally quicker than the GTD once rolling, the GTD is marginally quicker than a GTI when you add a DTUK box (worthwhile upgrade if you keep it!) and the power is far more accessible (you don't have to milk it on the upper end of teh rev range all the time to change pace). If you want something radically different, given your mileage then i'd get the R - confidence of no tramping is a good thing! If it wasn't for my mileage doubling with teh new job i'd have no regrets with the R at all. Driving the new A1 TDI half the time to work will help lessen that blow - getting a new job that I like and doesn't involve me going through the tolled Tyne tunnel would be the icing on the cake.
Going heavy on the extras will always hurt when you trade in, never felt the need to add extras to the GTD, and the R only got Prets because i'm not a fan of the Cadiz. The Pro unit is one hell of an extravagance given its price (will add almost £45 a month to a ypical 36 month PCP on the assumption it retains 20% of its purchase price if it's still around £1740).
3 options I would consider in your shoes:-
1. Keep the GTD as is, wait until the MK8 is out and trade in or (even better) sell privately.
2. Keep the GTD, add a DTUK box, new tyres (not Flintstones) to prevent tramping (or at least minimise it) and have GTI beating performance once rolling without the mpg penalty.
3. Go the whole hog and get an R for an extra 5mpg thirst over the GTI.