Personally, I wanted to get my interview out of the way on the soonest available date. The longer you wait, the longer youll be worrying about it. It is rolling admissions so the sooner you interview, the better chance you have of being admitted. Plus there really isnt that much of a difference in price in plane tickets if you fly in the next week or the next month. As far as being cynical, you shouldnt be! Midwestern decided you were qualified enough to want to interview you. You should be proud of that fact! Also, in Dean McCallians presentation before the interviews, he states that over 300 candidates are eventually offered acceptance out of ~385 that interview so your chances are really pretty good! The worst that can happen is you will get placed on the alternate list, which means you may eventually be accepted anyway.
Just bone up on the interview feedback portion of the site and practice, practice, practice giving genuine answers to your friends, family, or just yourself in the mirror! I did this and found I was much less nervous on interview day. If you know what youre going to say ahead of time, your delivery will be much smoother and more believable. Just try not to sound like your giving a canned response. Its a balancing act, but just try to sound sincere and you will do great!