Hey, Flagcarrier, from what I've read, there is no way to tighten the Air hinge. Some (presumably pretty bright) kid on another Mac site tore his apart, discovered how the hinges were made, and he seems to know his stuff enough to know there is no way to tighten the hinge. So, the only way they can tighten the hinge is to install new hinges, which means the whole lid/LCD panel piece, because that's the part kit. See if they are willing to do this. At least, if not, get the case logged so that if the hinges breaking is a direct result of wobbly hinges, and your hinge breaks, the problem has been noted, that you tried to have the wobbly hinge fixed.
I have to agree with you: Hard to even call this problem cosmetic as the only time you notice during normal use is when you reach up to adjust or close the display, it moves a little bit without resistance. Carl described it like the lid is flapping around like the cover of hardback book. Carl, it's nothing like that. It is barely noticeable. So unnoticeable, seriously, you can't tell if it's always been that way and you just noticed, or it has happened over time.