I would just keep the stock headers and use your money for maintenance. At some point your stock exhaust may need to be replaced due to rust, I'd make the decision then whether or not to get new headers (and probably a new cat) then, because you can do it all at one time. Welding is going to have to be done when you switch out the headers and the cat, so it would be best to sort out the entire exhaust system then.
If your system doesn't need to be replaced I would take off each bit, clean it out and repaint it. Cleaning out the cat will make the most difference in horsepower gains, and you get to keep the entire system bolt-on.