Welcome, and I have to agree with H5O, although I have actually added it myself because it gives me the option of switching ride-comfort. Unfortunately you are not going to find many people who have driven identical cars back-to-back, in identical conditions, just one with and one without ACC. So, you'll naturally get conflicting views and opinions on how perceptively good/bad it is. By all accounts, the new ACC on the new GTI offers appreciable differences in ride-quality, from very refined in comfort, to tight and sporty if that's what you want. Personally I want comfort over sportiness most of the time. It's certainly something I value far more than the PP, where under normal road driving conditions it offers me practically no benefits. With ACC I'll benefit every single time I drive the car, no matter where or how.
What JoeGTI said about not missing it if you never had it is true. Same can be said for the LSD in the PP, and even the car itself - you can't miss what you never had. Ultimately only you know what you want the car for and how you will drive it.