The thin superglue will find its way into the crack, almost rejoining the two sides and making it invisible. Nailpolish or lacquer will just coat the surface. If they're long like that I'll usually scrape along it with the corner of a razor blade to get a little "vee" groove so the glue flows in there better. You don't want to ask the glue to flow too deep because it won't. It will harden before it sucks its way all the way down. Then you're "locked out" for good. The groove gives you a little more glue surface to bond and buff when you're done. If you want, you can humidify the guitar in the bathroom with the shower going first. It was the expansion of the wood that cracked it in the first place. So if the wood is expanded, you should have an easier time getting the glue into the crack. That's just theory. It could make so little difference that its not worth it.