Are cold air intakes worth the cost?

I was thinking about putting a cold air intake on my maxima and was wondering if it was even worth the money? Do they give you that good of a boost in performance?

Not that you'll feel really. There are plusses and minuses to them.

Good things:
cleanable air filter
free flowing air filter (which will only help if your stock intake is restrictive)
Nice sound when you floor it

Bad things:
free flowing air filters don't filter quite as well
more noise if you don't like it
don't typically add much if any HP.

You can make one yourself if you feel like fabrication. Just keep the sensors and wires in about the same spot and make it from PVC, ABS, exhaust tubing, flexible RV sewer hose, dryer duct, or a combo of all of the above. Buy a big K&N cone filter and put it on the end. Some cars its really easy; others have a lot of bends and turns that make it tough.

I would suggest talking with some Maxima performance people/websites to find out if its worth it. Some cars like the new Duramax trucks can pick up an easy 15 hp with an aftermarket air cleaner. Some cars like the new BMWs are showing no change at all

I've been told that PVC is very bad to use under the hood. Something about it releasing chlorine gas at certain temperatures.

I'm not sure about the Maxima, but my B13 Sentra (GA16DE) has been shown to have a pretty restrictive intake and exhaust. I think a CAI adds up to 5 hp, which isn't much at all. I do like the sound of them, though. I may invest in one in the future.

Doesn't the Maxima have a KA24DE in it? I think you can turbo those fairly easily......

You don't have to do the pod filter part of a cold air intake.
You can just reroute the inlet into your existing filter housing. That keeps your existing sensors and everything nicely unmolested.

How much it'll help will depend (as Curtis has already pointed out) on the temperatures and pressures your current intake system is seeing.

If I remember correctly for every 10 degrees F you lower the intake temp you gain 1 hp. So the cold part depends on where the engine is getting it's air. I have seen too many kits get air from the engine bay (way too hot). Kiwibacon is on to something. Unless your intake is super restrictive you are better off getting a nice cold charge by rerouting you existing intake. But if it's the noise your after have at it.

If I remember correctly for every 10 degrees F you lower the intake temp you gain 1 hp. So the cold part depends on where the engine is getting it's air. I have seen too many kits get air from the engine bay (way too hot). Kiwibacon is on to something. Unless your intake is super restrictive you are better off getting a nice cold charge by rerouting you existing intake. But if it's the noise your after have at it.
Should be a percentage figure, if anything. It's like nature's boost.