Take it from someone who came from the Mustang world, save your money and stick with stock. It's well documented that intake air temps are cooler with closed element air boxes vs open element intakes. It's also well documented that the vast majority of power/torque increase in a CAI/tune combo comes from the tune, not the intake. Finally, in a naturally aspirated application, the stock air box is and never will be restrictive. An aftermarket intake that doesn't require a tune and costs several hundred dollars may net you 5hp and 5lb-ft at the wheels. You'll never notice it.
If you're interested in bumping your power and torque numbers, leave your stock air box and just get a tune. The absolute only time an aftermarket intake would become a good idea (read: still not necessary for most people) is in forced induction applications, where a stock soft rubber intake tube could collapse with enough boost boost, whereas a rigid plastic one won't.
