Yes, a cold air intake does aid in boosting horsepower. However, its effectiveness does vary from one vehicle to another. After all, you're changing the sometimes restrictive stock air filters with one that enables colder air to flow into the engine. In effect, colder air allows fuel to burn more efficiently, hence improving the rate of combustion. Thus, you'll most certainly see some horsepower boost, even if a little. If you install one on a typical 4-cylinder engine, you could see a boost of upward of 20hp. Meanwhile, a sportier and racier engine might see higher gains than that. So, it's a small increase, but not bad for its relatively low cost.