honestly, and i'm seriously being honest, keep the dx 1.5 or 1.6L non vetc motor stock. save your money and when you are ready do a motor swap to a more powerful vtec engine like the integra 1.8L or rsx type s 2.0 vtec motor. i think the motors are called B18, K20, D16 etc.. i'm not an import genious but i know its much cheaper to swap out the motor for something that makes 200hp than to spend three times as much trying to get your 100hp engine to hit the 200hp mark. there is alot of people that do this swap and too many knowlagable mechanics have the know hows to do a decent swap plus tunning for you for cheap.
to do what you are asking (wasting money in my opinon) CAI = cold air intake so Intake plus headers plus exhaust plus a high flow cat will free up about 10-18hp, nothing more than 20hp tho.
the benfit of your car being a dx is not much can go wrong with that car, most the stuff are manualy controled i.e. windows, locks, mirrors etc. so that makes it the lightest 4 door civic of that year, take away back seats and all that you can and you have the lightest car, weight to power ratio is key. so jump on that first take out whatever you can and whatever you don't use out of the car and save yourself some couple hundered pounds
so just a figure say ur car makes 100 hp and does a quarter mile in 18.000 seconds. and it weights 3000 lbs.
take away about say 300 pounds of weight, your car will make a quarter mile with same engine at about 17.5 seconds.
