The smooth tubes and filters look nice and they don't cost much so you might as well buy them. For improved sound you can do a muffler change. Others may disagree but I don't think you will feel any improvement if you put on headers. It will give you some extra power and you will see a few tenths at the drags but I don't think you could actually feel it. If you want to feel an improvement for less than the $7k supercharger kit, go for a reasonable size nitrous kit. A rear end change to 3.55 gears will give you the feel too. It might not improve your quarter mile times but it will feel more powerful for street driving. But like I said, others may disagree.