The problem is you're expecting the additional wonga you spent on extra's to be taken into account

I thought it was common knowledge that there are worth almost diddly squat when you come to sell a car. 1-2K max maybe - nowhere near 6K or so that you specced the car up to be.
I'll bet a 'bog standard' car wouldn't lose anywhere near as much over the same period.
So not wanting to be rude or anything but ...
a) You can't expect the extra's you added to be worth anything near like as much come resale (probably most folk just want 18's)
b) What the heck were you doing spending almost 27K on a golf for ... they are fantastic cars but 27K .. jeeso!
Try the resale on a 27K Mondeo or Vectra .. that'll make you wince

Avalyn.