A CAI is the most cost effective and safest way to increase performance. I've had one on my 2000 Prelude since it was new (well, 2 weeks old) and haven't had a problem with the car. Combined with a K&N filter it is as safe if not safer for your engine, considering K&N filters do a much better job of filtering than a conventional paper filter. At the same time, you let your engine breathe the way it is designed to. So you are not forcing anything into the engine, you are just letting it do its thing. As for voiding the warranty, there are federal and state laws which govern what a dealer can void and what they can't. In a nutshell, you can mod your car all you want and the warranty can't be voided unless the problem can be proven that it was caused by your mod and only by your mod. So, if you put a turbo, increase compression, and install a nitrous kit, then you have your car towed to your dealer because you broke a connecting rod, sure as hell they will void the warranty. But unless you drive through a 3 foot puddle and they can prove in a court of law that water got through the intake manifold (very unlikely since CAIs angle down), no need to worry about it.