Yes, you are right - the air being more dense as it's colder.

But the stock intake system pulls air from the front core support, isolated from the engine bay. This is essentially a cold air intake from the factory, but there is a rain/junk guard that could somewhat bottle neck it at high RPM.

At lot of these intakes I see being built/installed actually don't pull any fresh air from outside, but the hot air that's under the hood. Sort of going backwards on that one. Aftermarket "CAIs" can be done for sure, but very rarely do I ever see a good setup made that's superior (ram air) to how the stock system works.

Pete