The high flow discharge conversion kit just sounds cool. If you are on factory warantee, then this part is already covered, so you don't have to worry about blowing your blow off valve.
The Turbo Discharge Pipe and the Diverter Valve (not a blow off valve) are not related except they are both on the turbo.
Changing the discharge Pipe size wont have much of an effect if your stock or even stage 1. Now if your Stage 2 with an intake and all the toys then ya you'll notice some gains in the top end as it allows the turbo to move more air quicker.
I have heard the upgraded discharge pipe isn't worth it. I personally have the Neuspeed charge/throttle body pipe and feel it made a slight difference in throttle response.