Perhaps this song might convince you to stick with the GTI:
Ode to the GTi by Sir Cliff Richard
Words adapted by am1w
When I was young my father said
"Son I have something to say",
And what he told me I'll never forget
Until my dyin' day.
He said, "Son you are a GTi boy,
And that's the way to stay,
Son, you be a GTi boy until your dyin' day".
When I was sixteen I fell in love
With a girl as sweet as could be.
But I remembered just in time
What my daddy said to me.
He said, "Son you are a GTi boy,
And that's the way to stay.
Son, you be a GTi boy until your dyin' day."
Those are the words I needed to hear! Thanks Asker!!!

Exonian - where are you?
Sorry! Had a hellish few days working silly long hours but I'm here and admiring all the responses right now!
Well what can I say; thanks for all the opinions, advice, words of wisdom and most of all the p!ss taking (without which it just wouldn't be worth getting out of bed in the morning!)
I've taken a couple of cold showers now to calm my eagerness and thankfully being frantically busy at work has diluted my thoughts over the last few days.
In answer to various things put to me and in no particular order:
I don't owe anything on the GTI as I had a few coppers tucked down the back of the sofa so decided I'd put some of 'our' house moving fund to better use and bought the GTI before my darling wife cleaned out everything when we moved house.
The GTD would need a few grand throwing at it as my car is only worth about £19k now according to CAP despite having a very low mileage thanks to said house move meaning I hardly went anywhere this year and my other old runabout has been used as a mobile skip so had been doing all the mileage (probably hence why I needed a new battery at the grand age of 12 months).
My GTI is about 15 months old now so hardly an old rattler but with the 'new' GTD being pretty cheap for what it is I'd kind of hoped it would depreciate less in the next 12-18 months than my GTI and I'd probably also use it a lot more as to be honest my GTI has been an expensive and very dusty ornament lately.
The only options on the GTD is the poverty but still overpriced nav but my GTI was hardly specced to the hilt as I just put on it cheaper options aside from the PP to minimise depreciation - so RVC and 'miracle parking' are the only options aside from poverty nav.
And to Andy Wigit:

funnily enough as all of our work vehicles need the Diesel glove treatment and I still often use them for my petrol cars as the whole pump areas are often smeared with the yucky oily stuff. Ewwww! So I keep a load of Diesel gloves (borrowed from work) in my car as it is!
I'll whisper the next bit quietly
Your R isn't quite standard and I wouldn't mind betting a standard one wouldn't set your world on fire! 
Anyway, keep the abuse coming everybody as I'm still thinking about it!