We were also living overseas when our DD got her appointment. We did not make an extra trip back to visit the school again. In fact, DD's visit had been the summer before her Junior year of high school. While it may be nice to attend the open house, it is by no means necessary. My first full tour of KP was when I brought DD at Indoc. (Can it really be almost 4 years ago?) My husband did't get to visit at all until Parents Weekend.
If time and money are not a problem, then go to the open house. But don't worry about it if you can't visit again before your DD reports to Indoc. The event you must not miss, if at all possible, is Parents Weekend! Contact the Parents Association chapter that serves the state from which your DD got her nomination. They can answer questions and will give you a chance to get to know some other parents. If you are Stateside for their Welcome Aboard event, that's another "nice to attend" event where your DD can meet other candidates and you can meet other parents.
The biggest hurdle with being overseas will be things like getting the TWIC card. Finding the correct supplies, running shorts, shoes, etc. can also be a challenge from overseas. It can take longer when you're overseas to do things that are routine here in the States. Don't be afraid to contact the Admissions Office and the Parents Association to try to get a head start on the process.
Good luck! And if you have any questions about heading to KP from overseas, feel free to contact me.