Ok I dont have much experience with Computer Controlled vehicles, but from increasing HP on Quads, dirtbikes and such. What I would do if you plan on spending money is get a turbocharger on that engine, they are the most efficient thing you can do. You mentioned you looked them up at howstuffworks.com so you know this already. Now If you have a turbocharger open up that intake, what you need to do is dont worry about all these overpriced cold intake 'kits' and such and go and find a filter with the largest surface area that you can fit under your hood, Go with a round, take some furnace duct and put it around it, seal it off around the filter, then cut a hole in there enough for a good sized metal tube 4" should do it, then direct this tube to a place where it will be getting forced air from outside your engine bay. You now have the best intake you could probably do for usually under $100. Also do not go with K&N, as far as flow and filtration they compare to running no filter at all, too much **** goes through them. Instead go with a company like UNI and if you want paper theres Donaldson, WIX, Fleetguard etc etc. Now that you have your intake covered, and since you have a turbo, you dont have to worry about backpressure too much, so just run a good sized pipe going straight back on the system, if your worried about noise, get a straight through muffler. Also when running pipe, make sure to get all Mandrel Bends, Crimping = Stupid and bad. Now that you have the intake and exahust covered, your engine is breathing nicely. Well, this would be the point where you would have to fool your computer some how with a chip or whatever, I cant suggest much on this because I dont deal with computers. After you have fooled it and you are still power hungary I would go with an aftermarket camshaft, usually you will have the potential for better fuel economy, and will definately have more power for the price. Then I dont know much about NOS but I do know that it cools the air down and makes it dense which is good (your engine wants cool dense air for a more complete combustion) so if you didnt go too crazy and bought a system it is a very cheap HP upgrade. After this you should be making some descent HP and still driving everyday with good Fuel economy. But like I said, Im not much into gassers or electronics. On my truck everything is mechanical and there are a few such steps to take when upgrading and its not hard to triple the HP and TQ.
My best suggestion for you would be to find a forum like this that is dedicated to your Type of car and see what they are all running and their luck.
Good luck with your search.