Yes, there will be lots of interesting panels, swag, premieres, celebrities and other stuff at Comic-Con. Whatever. Nintendo just gave us the real reason the July 22-25 event is worth attending: a new Dragon Quest IX map. If you bring your DS to Nintendo's booth, with the game running in Tag Mode, you'll automatically pick up the "Mortamor" treasure map, being offered for the first time in North America. Presumably, other people will be there doing the same thing, making it your best chance at multiplayer. If you aren't playing DQIX yet, you'll be able to spend some demo time with it at the booth (#2944).
You'll also get the opportunity to play Metroid: Other M, over a month before its August 31 release. Now that's an opportunity worth fighting the cosplaying crowd for.