Easy mods would be to remove the air silencer and add a K&N panel filter. You could also go with a CAI (cold air intake) such a MAC. These usually run around $180. The K&N is less than $50. Other than that, I would recommend you do something with the exhaust. At least replace the resonator! Take a good look at the pinch on the pipes exiting the resonator, yikes!
JFYI: ATX refers to the term "automatic transaxle" which would relate to FWD cars, MTX being "manual transaxel". RWD cars are just "automatic transmission" or "manual transmission". You musta been hanging around the SHO guys on on SHOForum. It took me a while to get adjusted with the terms, just about every post over there uses either MTX or ATX and over here you never see those acronyms.