Cold air and more air sound good in theory, but no one gives a hill of beans about theory when you're trying to pass someone on the highway.
The good news is that although claims of actual horsepower and even increased fuel efficiency may vary, cold air intakes will in fact help increase your car's performance.
By itself, you'll probably notice an increase in power when the throttle is fully open. Some manufacturers claim as much as a 5- to 20-horsepower increase for their system. But if you team up the cold air intake with other engine modifications, like a new exhaust, you'll create a much more efficient system. So think of it as just one part of many to increase your engine's performance.
There are a few drawbacks to consider when installing a cold air intake though. If the air filter is too exposed and sucks up water, it'll go straight into your engine and you'll be up a creek. Pun intended. Look into adding a bypass valve to keep this from happening.
Also, installing a cold air intake on some newer cars may void the engine manufacturer's warranty. So look into this situation before starting, or at least understand that it could become a problem later on.
Other than that, install that cold air intake and hear the magnificent sound of free-flowing cool air to your engine -- and enjoy a few extra horsepower as well. It may be just what your engine needs.