Not specific to the GTI, but in general terms I'd only spring for ACC if the car will be shared with another driver or used for two greatly different scenarios.
My 4WD has adjustable springs and on that car they're brilliant, because we drive it in Comfort when our baby is on board and can switch to Sport when I take it to the track, so our enjoyment of the car is improved by being able to adapt the suspension to those different uses.
I've got fully adjustable Bilsteins on my Polo, but as I'm really the only person to drive it and I like the firm ride I've never actually adjusted them - they're just set on fully hard and left that way.
If you're going to be the only driver of the GTI and you don't have a family I wouldn't worry about the ACC. If you want a firmer ride on the standard springs then spend a fraction of the cost of the ACC to tune the suspension to your particular liking, and leave it as such.
If you have a family (such that you like the Sport setting when driving by yourself but Comfort with the kids in tow) then the ACC will be worth its weight in gold (and spousal approval).
What ever you do don't turn a great car thats fun to drive into one thats a PITA on long hauls .If I was looking at club racing coils overs might have been my choice .
Ordered mine with ACC .
Cheers
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