I may be wrong but isn't the engine in the GTI oriented differently than in A4s? That could be the reason you don't hear the DV so well. It's on the other side of the engine, vs right next to (infront of?) you.

 

Springs wear out, thats another reason to buy the kit.

Not really, the DV noise is heard through the intake, it doesnt matter where the DV is actually located. You could reroute the dv to your trunk and youd still only hear it from the air intake right next to the engine.
If it was a BOV, that would be different... And Im sure I'll be sorry I even brought that up [:@]