VirginVWman:
Keeping a car less than 2 years will always kick you in the pocket. The dealer's profit margin in selling it on again is going to be 15-20%. If they'd put a sticker price of £24k on it in the used forecourt, then it is likely to attract a p/x price of £19-20k.
What is it about the GTI that attracts more? The red stripes? The low end performance (from a standstill)? The in gear performance (not massively better than a GTD), the "GTI" badge? Can't do much about the low end performance, the GTD will always struggle to put it's power and torque down from a standstill (just look at how a Quattro equipped A3 184TDI shaves 0.5s off the 0-62 time vs the 2WD variant).
The DTUK box has transformed my GTD. You only need to tickle the throttle to drive it normally, and when you want to put your foot down on the move, you will never find it lacking. My GTD was a disappointment next to my Scirocco 170TDI. How could the GTD have 8.5% more torque and have less grunt in 5th and 6th than my Scirocco, considering it is geared the same (2200rpm in 6th @ 80mph in both cars)? It is a smidge slower and a lot less fun to drive in standard guise than my Scirocco was. Best £359 I have ever spent towards a car, it has been transformed.
Why not ask Andrew at DTUK to trial a CRDT2, setting 4+1. I bet you'll lose the disappointment and regret you're currently feeling.