In addition to soaking one's liver with tequila, you can also soak in some of the local culture. Dancers perform traditional dances at the expo and there are also numerous vendors selling food (not many vegetarian options yet). I loved the mariachis and the chance to practice my "laugh." My uncle's aunt can do it well but then again, she was raised doing it. I will master it one of these days.
I was unable to make it this year but I am almost positive I will make next year's. Admission is $5USD and you get to sample plenty of tequila as you walk past the vendors. Everyone is willing to give you a small sample and it's likely you may stagger a bit upon leaving. I know Mexico has its problems right now but I came specifically for the expo. I'd been before just by accident and was excited to go back. I suggest you bring a designated driver and if possible, park your car on the outside of the border at one of the parking lots w/ available bus ride into the city. It's cheap and easy, and you'll probably feel better about leaving your car on the US side if that concerns you. We like it simply because it's quicker to enter the border.