A little late in linking to this, but my former boss Paul Oberjuerge wrote about US-Mexico and it's worth reading no matter how far removed from the game we are. Paul has a great perspective on the game as he has covered many US games in his day, including the US-Mexico game in Azteca in 1997.
Anyway, Paul offers his thoughts on the match here.
One of his first thoughts...
"Once we get past the instinctive 'beating Mexico is always good news' … it occurs to us that Mexico is barely a worthy opponent anymore. The American team is getting better, yes … but Mexico seems to be regressing into fairly thorough mediocrity."