Welcome to Just Commodores, a site specifically designed for all people who share the same passion as yourself.
What you guys dont seem to know or are forgetting, is that the warranty that walkinshaw supplies IS NOT backed up Holden they just acknowledge it. If anything stuffs up Walkinshaw fix it on their end & if you have engine failure you would be hard pressed to get Holden to supply you a new engine under warranty, its walkinshaw who have to fork out for a new one & they can be real pains to deal with with warranty work(ive seen it before).
Im not saying dont modify your car but walkinshaw charge way too much for what they supply(and personally the warranty isnt worth the money), you can get a good quality exhaust, cai otr & custom tune suited to your car(not generic like walkinshaw use) for alot less you just gotta shop around and find a good reputable performance workshop.