The only valid reason that I can fully understand and accept that you would choose a GTD over a GTI is for efficiency and economical reasons. Choosing it over the GTI based on aesthetics makes absolutely no sense to me whatsoever given that they are near identical.
I primarily chose the GTD over the GTI for a £110 a month saving all in - between residuals, road tax and fuel economy, it added up to about that in the early days. Now the residual differences are out of the window because the diminished residuals of the GTD, although still higher than that of the GTI, are cancelled out by the deposit contribution the GTI gets.
Now i'm in the R, it costs about £80 a month more to fuel, but personal circumstances have changed and i'm a 100% cash buyer (used to be a PCPer prior to the GTD which was bought with a loan off my Dad at the rate he would've got via an ISA - 2.8%), so the interest savings are more than subsidising the extra fuel. I don't like the Austin wheels, and I really don't like the Cadiz, but I wouldn't let the wheel design dictate the car I bought.
An options tightarse like me was willing to spend £895 on Prets so as not to have the Cadiz rather than discount the car based on the look of its wheels. I slightly prefer the GTD's lack of lipstick, but you'd not notice them on a TR GTI.
It's not always about being tight on fuel costs alone, some prefer the low down torque of a TDI - to be honest I think if they made an R TDI with 270PS or more, I may be tempted. It takes some getting used to milking the R to get anything out of it you wouldn't get by driving the GTD hard, but I had some fun today on the way home, screaming away from a standstill at a traffic lighted roundabout up 2 sliproads.
Right now the GTD won't save you much against a GTI when doing lowish miles, but money is not the only reason to pick it over the GTI. People bang on about rattly tractors, but the truth is that once you're rolling, the GTI and R are just as noisy on acceleration and the GTD is a quieter cruiser because of it's higher gearing
