Performance

Hi Again, I was hoping for a bit of advice regarding the enhancement of my 2003 Grand Am GT. I have heard both sides of the story regarding the K & N air filters....any thoughts? As well, what other little things can I do to improve on performance. I do realize that exhaust plays a part, but what about changing the plugs, or the plug wires, or anything else under the hood. Appreciate all your comments. Cheers.