Well I added the following to my GTD and I've listed below if I would take them again (in no particular order):
DSG Gearbox Yes absolutely, aside from the fact that my wife (due to a dodgy left knee) can't properly drive a manual any more, I love it - super smooth and really quick changes. YMMV
Rear View CameraAbsolutely - makes reversing during the day or night (especially at night) a real doddle.
ACC (adaptive chassis control)My last Scirocco had this but to be honest I always found it very subtle and quite difficult to tell the modes apart. Wasn't going to spec this until I test drive a MK7 Golf fitted with it (on 18" Alloys). I could now at last really tell the difference. Normal is just perfect for everyday use, Sport when you are feeling naughty (and to be honest doesn't firm up to the point of being uncomfortable), but comfort - that turns this hot(ish) diesel hatch into a limousine, with an impeccable ride (especially given the wheels), and makes the car a perfect long distance cruiser in supreme comfort. Also good for round my way where the roads are shocking !
Discover Nav ProI do like having Nav built in and the Pro version does bring some real advantages (especially the screen size and resolution), but if I was doing it again, I'd probably spec the standard Discover Navigation instead - the Pro whilst good is just far too much money in hindsight (but it does finish the dash off nicely).
Park AssistReally does work and is quite spooky at how good it does work. It was so cheap (relatively speaking) that yes, I'd probably go for this again.
KeylessWasn't sure about this at first, but now after a year I find it weird getting into a car without it. No messing with keys or struggling in the rain, just touch the handle and jump in. Also can't beat a nice big "START" button
Main beam assistAgain another real cheap option, but I'd actually opted for lane assist (to get the traffic sign recognition) and it came bundled but some months after ordering it VW decided I couldn't spec it on a GTD so they removed it but left the main beam assist on. On it's own its nice and cheap and does work quite well, but I'd probably leave this off next time.
Winter packDeffo yes. Quite expensive for what it is on a GTI / GTD (basically just heated seats as the GTD/GTI/R gets headlight washers and low washer fluid warning as standard), but it's so nice in winter to have a warm bum and back when it's freezing outside (especially when you reach my age).
DynaudioNever heard the standard set up but as I love my music on the go, this was one of the first options I ticked. People are divided it seems on it's effectiveness, but it's worlds apart from my MK5 Golf and Scirocco that I had before the GTD. Good dollops of bass but enough finesse to reach crystal clear highs.
Other items I considered :
Santiago 19" alloys - look stunning but at nearly a grand was a very expensive option and much dearer on the tyres (but did I say they looked the mutts nuts).
Leather - was really 50/50 on this one. Whilst I love the look of leather and the quality feel it exudes, it's was far too expensive in my view (is there a theme here

), and having experienced previous VW's with leather found the squabs and bolsters went saggy after a short way and subject to cracking mainly on the bolsters. Don't know how the MK7 leather is fairing, i.e. if it's better quality. Also don't like the cold feel in the winter and stickyness and red hot in the summer. What I would really have liked is part leather like in some markets that retain the cloth backrest and squab (the bits your body mainly touches), but leather elsewhere - but sadly not for the UK.
Climate Windscreen - This was added after my car was ordered so not an option at the time. Liked the idea but not the price of a replacement @ £1200, if your insurance company doesn't cover it, and to be honest, not really had a problem with no having it.
About the only thing I would change is the colour. I have a pure white GTD which I umm'd and err'd about, but in hindsight should have gone for either Red or CSG (there are so many white GTI / GTD's where I live now).
That's about it, hope this helps.