A CAI is worth it to you if you want a little extra sound and a little more throttle response. If not then don't get it.
If you are worried about your warranty, don't ever mod your car. It's pretty simple really.
As for switching back to stock parts for warranty work, well that's fraud, dealers aren't that stupid, and you'll go to jail if you get caught. Have fun with that. If you hydrolock, it's not going to be covered by warranty anyway. That falls under the "you were stupid and broke your car" category, not warranty work.
Repopulating yourcobalt.com one post at a time.