Damn it Norbreck ive too and froed about ordering it and then finally decided not to. Now after reading your post im back in two minds. i intend to keep my gtd for at least 5 years (I said the same about the R Line Tiguan and thats going after 9 months!) I dont want to start going down retro fit routes and I suspect you probably cant with the adaptive chassis control anyway. Does it make that much difference having the chassis control??
There have been a few posts from chaps who had mk6 without ACC and say the car is great with or without it, but mostly they'd spec it this time round. Roc drivers get it as standard and say the car is great, but we have nothing to compare to in this case. Hard to know. The reviewers rate ACC and PP very highly, but again they haven't been driving both with and without (or they are keeping it quiet if they have) so how do they know?
I think its like Gryzor says, you want to feel happy with your choice. So if you'll regret it I'd say get it even if the sales guy is right about it not being worth it. If the cost is too high then stay clear, you don't want to be feeling like you were ripped off.
Logically the ACC and even more so the PP will not be of any real use to 99% of your driving. But if you want to go flying around corners and know you are doing so in a car no rival can do better then grab PP, and if you want to know you're driving a car that can do sporty and super comfort at the flick of a button grab ACC.
EDIT:
This post and the thread in general have quite a few experiences of ACC posted:
http://www.golfgtiforum.co.uk/index.php?topic=252900.msg2319977#msg2319977