I have an 02 3.4l and installed and made an intake for mine and helped a little but the biggest difference was the sound. It sounds so mean when accelerating. You should gain about 12 hp at the flywheel. Improve gas milage a little but i havent gotten to check that beacuse i cant keep my foot out of the gas.
You wont see much of an increase. They all claim to add horsepower but in real life practice you'd be lucky to get 5-10 HP at the wheels. For the amount of money you'd end up spending on it, I wouldn't consider it as worthwhile. The only intake like that that makes a big difference is cowl induction on older cars, and only when they have the rubber separator around the air filter. That way it only sucks cold air compressed at the base of the windshield. And even then, it only makes a noticeable difference at high speeds. You'd have better luck getting power working on your exhaust etc. first.