I went business casual for my meeting at a neighborhood Starbucks on a Saturday morning. In my opinion, demonstrating your ability to adapt to different environments and transition between them is a sign of confidence and maturity. At a place like Kellogg where soft people skills are sought after, understanding and predicting social convention is somewhat important. I felt that if I had arrived in full battle gear it could have been taken as my inability to "fit" the situation. Maybe I'm over thinking this, but it isn't a secret that business formal is the default option if you don't know what else to wear. The last thing I wanted was to be viewed as unsure. I decided to take a calculated risk and I think it worked out. My interviewer was full casual and I'm pretty sure my slacks and dress shirt didn't raise any red flags indicating I was inappropriately over- or under- dressed. Unfortunately, there is no way to be sure of this claim, but I would wager my application fee that my interview attire will have no material impact on my admission decision. (If you can determine whether I get in or don't based on this criteria, please take me up on the $250)
I'm probably full of it, and you don't need to hear my paranoid pontifications, but this was the way I approached the "interview attire" question for Kellogg. All else aside, if the interview had been on a weekday, I would have suited up without a second thought.
ps-Use linkedin to create an information advantage. Don't walk blindly into a meeting. Do your best to prepare for who you're going to meet, as well as what they will ask.