If you already scheduled your interview at this top school, I would not reschedule it unless absolutely necessary. "Wanting more practice" is not a valid reason, and you should have looked into flight prices before deciding on a date.
If it's any consolation, I'll be doing my interview at my top choice school second. Sure, I'll be kind of inexperienced at medical school interviews when I interview at my top choice, but I figure I'll just do my best and let the chips fall where they may.
One could argue that you would do better with the MMI interviews early in the cycle, before you get bored and jaded.
If each MMI has 10 stations, then by the fourth school, you will already have had 30 episodes. By then you will find it tedious, and it might show.
Just look online and read a book on MMI to get an idea of what to expect, and go in fresh and enjoy the process. If you go in with an open mind and consider it a fun challenge you will do your best.
Never had to do any of this MMI business, but my top choice school before interviews was no longer my top choice after I was done interviewing. I wouldn't put too much effort into rearranging your schedule based on what your dream school is now. Just prepare for all of them as best you can.
There's something to be said for being familiar with the format. After my first MMI, all subsequent MMIs felt less intimidating. It can vary dramatically between schools in terms of format, questions, and how tightly regulated it is. Best advice is to probably to do whatever makes you feel most comfortable. Interviewing a month later is unlikely to change anything about the consideration of your application is the consensus on this forum, I think.