If you will own the car a long time- it will save you money and will be good for the environment since you can reuse it.
HP gains- not likely on a stock car. Studies have shown HP increase from a K&N only after better headers were installed.
Be very careful of installing any filter that changes where the air is pulled from. Any filter assembly that is allowed to pull hot air from the radiator or engine compartment will loose horsepower due to the increased air temperature. Hince the name- cold air intake. It must actually pull cold air from outside the car. If you are replacing the entire air intake system with a well designed Cold Air Intake- then yes- you will most likely see some increases in Horsepower with some as high as 15hp.