Well, that's an interesting question!
If I were in your shoes, I would probably mention at an opportune moment in the interview that I am a reapplicant. Mentioning this fact will help you not just earn brownie points for honesty but also give you the opportunity to explain how you have improved your candidacy. The reapplicant essays are generally small 300~400 words, the interview might give you the chance to elaborate on a lot of things that you couldn't fit in due to word limits.
Further, I don't want the interviewer to end up with the impression that I am a first-time applicant and write something to that effect in the report he/she submits. I'm sure such a report would be viewed quite suspiciously by ad-com members (who know you are a reapplicant) who would evaluate your application along with your interview report.
Finally, it also depends on who the interviewer is. If it is an ad-com member, I will definitely state that I'm a reapplicant, whereas if it is an alum, I might not sweat not telling that I'm a reapplicant.
But anyway, these are just random thoughts. I am curious to know what current students and alums think about this...