Notionally they're worth some decent money (£60-100?), but I struggled to find a scrappie who would give me cash for mine...I'm sure Arnie can find a car to bolt them to though
I weighed in my Monaro's old cats for about £65 about 2 years ago, so well worth finding a scrapie who'll take them near you. VXR stubby headers always seem to sell quickly on ebay or the like.
If you have room, keep them. Prices are low at the moment, and you won't get much for them, but metal prices went crazy a couple of years ago, and should again.
Cheers... Sadly I dumped the headers... didn't think they'll be worth squat... but I've got enough room in the garage to keep the pipes/cats... for the moment!