Glad to hear you liked the interview day! Even though UCI's interview day is rather long, I think they do it so you can get a good idea of the school and have more opportunities to personally interact with students. If I were you I would definitely take advantage of the student host program! Seriously if you stay with a host, go to the dinner at Gina's, and get your questions answered at the student panel you shouldn't have any problem conveying your excitement about UCI in your interviews! The interview day here was definitely my favorite last year... it really blew me away and made UCI my top choice.
I'm a current MS1 and there's nowhere else I would rather be than UCI. Also, referring to the comment above about putting a smile on for an hour (which is a totally valid concern!): That is truly not the case here. People have their little complaints but we all really do love it here. UCI really has a family atmosphere and I couldn't be happier with my classmates, the faculty, and the opportunities available to me here. Thats why (ok.. along with the free food) so many students line up to come to the preinterview dinner, host interviewees, interview, give campus tours, and participate in the student panel-we want to convey how happy we are here, and help choose future colleagues to join the UCI family.
If anyone has any questions for a current MS1, don't hesitate to ask me!