I have a set of HKS Intercooler/hard pipe upgrade in
my GTO, and I like it.
If they're almost brand new for $1000 I say go for it,
because brand new the hard pipe alone is $700, eventhough
it is very expensive, but the pipes are mandrel bend, compare to some others, which are not mandrel bend pipes. The intercooler
is made with high quality welding and design, it is $1500 for brand
new! Total=$2200 from NOPI vs almost brand new $1000.
Too bad I don't have any data numbers so far, and without
bigger turbo, you really can't feel any difference other than
better boost response, and when doing repeated acceleration
especially on a hot weather it really helps!

The intercooler
will help alot if you have a bigger turbo.
hope this helps!
TL