Honestly, it depends how you use the car....PS4 S have a relatively softer side wall than a Cup2, and with Standard suspension on 18"'s, the car should be fairly compliant on the road.....if you are not going to track it, it sounds ideal?
As and when the shocks need replacing, it may make sense to upgrade? On a non GTi I have heard good things about Koni special active shocks on standard springs, which are compliant at lower speeds and harden up with load.....it's all subjective.
My own CS is 3 door, manual, buckets, Dcc & 19"s, I am happy enough with the suspension option of the Dcc, I will upgrade the tyres as the next step as and when they are needed.