if you can make it to the campus, you can visit the school, sit in a class and talk to current students. This will help you better understand what the school can offer. In terms of chance to get in, I don't see much a difference.
For interview(on-campus or alumni) conducted in the US, I heard that the admission committee may begin to review your application, once the interview is done(instead of reviewing all applicants all together between 12/04/08 to 12/22/08). It may give some advantage to applicants who conduct the interviews earlier than the others. I am not sure this is true, will you please confirm? For Chinese passport holders in the US, do they belong to the Chinese applicants pool or the American applicants pool? Thank you.