Will aftermarket headers add a significant amount of gain? If so which would you prefer?

 

headers don't really do anything on a stock v6.

 

so it would a waste of money? ok. thanks.

 

Pretty much, unless your stock headers are severly rusted, leaking at the gaskets on the heads, leaking at the o rings that tie it into the mid pipe they're pretty much worthless other than a few engine stability avantages they offer.