I can't think of any other way to say this - springs are supposed to bounce! Dampers are supposed to control that bounce, if the car is bouncy or wallowy then the dampers aren't doing their job.
The std shocks on a GTi are poor at best but if the car has been fitted with lowered springs they WILL be sh*gged. If you've got some uprated and lowered springs then change the dampers first. If you want a stiff hard ride then get stiff dampers, 'cos if you get stiffer springs and still don't change the dampers then the main fault will still be there and you'll have a car that crashes AND wallows.
If you want to change the springs to change the ride height then fine, but don't change them 'cos they're bouncy - it's what they're supposed to do. I've worked on various competition cars including tarmac and gravel rally cars and off-road racers so I do speak from experience.
As I've said there's absolutely nothing wrong with Eibach springs, after all I've got some[

] but the dampers are the key point in the suspension. I know Pi haven't got the same car park appeal as Eibachs, but I'm sure that if they're fitted with some good dampers you'll really feel the difference. Even on a standard car if it's the only thing you change the dampers will give the biggest single improvement in ride and handling you can buy.
Sorry to sound like I'm preaching, but I've made these mistakes before and am just trying to save you some money.