I think your probably looking around £8500-£9000 because of the milage.
Mods wont add any value unless you get someone willing to pay for them,
Sell any removable mods seperatly and your possibly looking up to 10k depending on what you've got, you'd be better off looking for a set of standard sport alloys probably around £200-£250 with usable tyres if your lucky and sell your wheels on.
Plus people are always looking for debadged grilles. Suspension/Exhaust depends on how much it would cost to remove it (if your not doing it yourself) to how much you could get selling it for.
My g/f is picking up a 2003 FSI Sport in a couple of weeks 23000 miles on the clock for £7500 so that should give you an idea of how much they go for.
Lovely looking car though
James.
anyway if your getting a merc you could probably afford to give it away
