Just baffles my why a private buyer who does average mileage a year would choose it over the GTI given the initial purchase price and resultant relative loss in depreciation.
It's not a matter of a couple of hundred quid between the GTI and GTD, it's £3k over 3 years or 20% of the 3 year cost of ownership to do 99% of what a GTI can do on a public highway without risking the wrath of the bobbies. For those that dote on their cars the GTI might be money well spent.
Everytime I buy another VW I stretch what I am prepared to pay for car ownership (they have done the sensible thing with the MK7 by not increasing the prices significantly again - they were almost in Audi territory).
It's great to have a nice car, but not to the detriment of having enough money to do the other things I enjoy doing besides driving. GTI ownership would cost me as much as my mortgage and I can get nigh on the same everyday experience in a GTD for a grand a year less. It is purely head over heart. I have the money to run a GTI but would get more enjoyment spending the difference elsewhere than for the marginal gains.
My neighbour has a Scirocco R. He has a great car, and no life. It rapes his wallet on a monthly basis, costs him about £200 a month more than mine costs me (fuel economy half of what mine is, insurance and shocking depreciation as they're barely worth more than the standard 2.0TSI/210ps GT on the used market) and he earns less. He's always too skint to go down the pub or on holiday, but he seems happy enough with the situation he has put himself in. You've got to decide what's important to you with the money you've got. My car isn't my world, but I do enjoy having one I consider to be very good.
The GTI badge means a lot less than it used to. It's not the best/fastest Golf VW do, it's not even that fast against it's competition (when you are splitting hairs about 0.whatever of a second). it's a trim level (and a high one at that). It's so refined now that it isn't that thrilling a ride, it is very clinical and safe unless you are able to put it through it's paces at a track (I wouldn't be pushing any car of mine to it's limits on a track - have you seen the price of 18" tyres?

).
I liken it to rollercoasters. Those well built and shiny ones at Alton towers aren't nearly as scary as those rickety old and badley maintained ones you see at dilapidated seaside towns that go 1/2 as fast.
Pick a GTD with your head, pick a GTI if badge kudos and moderately greater power/dislike of Diesel are more important to you. The performance penalty on a GTD is very small in everyday use, for me the GTD gives more bang for my buck. Not everyone buying a GTD is wishing they had a GTI.
I'm sure almost everyone will be pleased with whatever they pick, it is the undecided that have the most to lose - I think most here have ordered the car they want (for a variety of reasons) and if VW did mmore to deliver them then they'd spend less time wondering (should I add ACC, should I change colour etc). Once you're behind the wheel hopefully you'll be happy enough with what you ended up with (apart from that windscreen wiper smear pissing you off no matter what MK7 Golf model you are in).