Multiple Acceptance Offers?

I was in a similar situation, except interviewing at a better school after I'd already been accepted at a good MSTP. No one asked me if I'd been accepted to a school... the "where else have you interviewed?" question came up a lot, and I mentioned the school where I was accepted and what I liked and didn't like about it, but never said I'd been accepted. I don't think they'll put you on the spot and ask about an acceptance and bringing up an acceptance without being prompted can make you sound like you're gloating. Mentioning and acceptance is hard to pull-off, and, in my opinion, it's better not to let it possibly hurt you.

As far as going to other interviews just so you can say you were accepted to multiple schools... I think not going is common sense. It would be a waste of money and time unless you might actually attend the school. I cancelled 4 interviews after getting in because I wouldn't go to those schools over the one that accepted me.

 

it's been a while since i interviewed for mstp programs but i don't think multiple acceptances at lower tier schools will make you more attractive to your preferred schools. i doubt it would have any effect at all and i think you would probably be wasting your time. the most you would get out of it is to meet some of the faculty at the other schools.
interview season is a stressful time, i would not go to any interviews at schools that are less preferable than the one you have already gotten into. take the extra time to rest, think about your other interviews and come up with other substantial ways to make yourself more attractive to your top choice schools.
feel free to contact me with any questions.