In terms of being prepared, I wouldn't worry so much about the class. The chances that you will really have to be involved are very slim, and not being prepared won't hurt your admittance chances. You'd have to make a major @ss of yourself for it to get back to the adcom.
But do be prepared for the visit. If you can get face-time with admissions people, that's good. If you have good questions for them, that's good. You want to see smart, interested, and together to everyone you meet. And by being prepared, you'll get more out of the visit. What matters to you? What do you need to know about the school?
I visited Cornell about a year before applying - it was a very early visit, and it was so I could learn about b-school in general. The visit wasn't to learn about Cornell, and I didn't learn much that would help me in that department. But later, when I went as part of the application process, I had a lot of questions ready to go, so that I could make a more informed decision later.