I have an all original 2005 GT, I just replaced the exhaust with a Granitelli Motorsport SS 2.5 Exhaust. How improtant is it to save the original exhaust pipe and cat back mufflers?
With the kind of production numbers the S197 has seen, combined with as long as modern cars are kept these days it's not very likely an ordinary '05-'09 GT will be much of a collectable where an original exhaust system will hold much value, at least not in next 10 or 20 years. In 40 years who knows, I know a couple guys who'd give their left nut for an original, unbent, unrusted exhaust system from a '69 or '70, but even with that example there's aftermarket duplicates of the original that's perfectly acceptable for use in a restoration which limits the actual $ value originals will have. So, unless you feel like hoarding those pipes for the next 50 years (and keeping them in perfect condition while you're at it), I think you're safe to unload them. Try craigslist, I'd bet there's plenty of V6 owners willing to take them off your hands for their dual exhaust conversion.