3sx downpipe + test pipe with the stock catback sounds great. Long tube headers sound and perform better but they're a difficult install and make your car hard to work on. I wouldn't recommend the headers unless you're really in it for the performance. The 3sx downpipe sounds great with a test pipe though, especially at 4000rpm and up, when the vic system in the intake manifold opens up!

As far as cleaning the stock tips I've had good luck spraying them down with Purple Power and pressure washing them, mine come out perfect on the outside. The center I have to hit with a small wire brush wheel on a drill.