A tune is way more performance than a CAI, BUT you're still under warranty and some dealers can be prickly about tunes when it comes to drive train problems.
CAI isn't going to do a lot from stand point of torque or acceleration. You wont spin 20"s on dry pavement just by adding one. It is however an obvious and satisfying way of personalizing your vehicle and one of the easiest DIY alterations out there. Depending on which unit, you'll get a little throttle noise under the hood, some improvement in pedal response, and you may feel a little sump'n in the butt dyno.
Sure you can restore to stock and flash the PCM before service with a tune, but that doesn't always work with a break down, and each time you flash your PCM it leaves a signature behind.
You may be fine vis-a-vis tuner and warranty. I'm coming up on the end of my 5/100 warranty and have only had one issue, an exhaust manifold. So I could have gotten by with a tuner, but who is to say I wouldn't have put more strain on something given the ability to jump on it harder?
As an alternative to a tune, I would suggest the pedal commander (see Moe's Performance). It doesn't mess with your PCM/Warranty and it lets you take a lot of the lag out of your pedal, making for a more responsive skinny pedal.