It sucks that I won't be able to participate in this. I guess all I can hope for is that the winner won't be using a 3rd Party Character. Even if it's Toon Link, Sheik, Link, or Fox that wins I'll find it much better than Sonic or Snake winning. Then again, with Sonic's high vulnerability to Shield Grabs and his lack of extremely powerful finishing moves and Snake's unique fighting style compared to other characters (like relying mainly on his explosives for his smashes and not melee attacks which will make him hard to master) it'll probably be somewhat unlikely that those two will win the tournament.
Taking your girlfriend with you doesn't sound like that bad of an idea unless she's really that against it. I mean if girlfriends ask you to go shopping with them for clothes every now and then, I don't see why they wouldn't be okay with going to this, especially considering it's a one time thing. Also, good luck with her.