Complete waste of time. The best option if you want to swap out your exhaust would be to go to a freer flowing single exhaust. The guy at the muffler place would prefer you go duals so he can charge you more. My guess is that even if you went with a single exhaust, he'd still charge you the same amount.
Not sure how you drive your vehicle but for a daily driver, a freer flowing exhaust isn't going to have an appreciable effect. If you off-road at all the additional exhaust tubing becomes one more thing to scrape and bang on rocks.
Finalyy, f you are just going for a cool sound the single exhaust is more than capable of giving you this. I wouldn't bother myself.