You have a basic understanding of orbital mechanics. That is important and good, since it shows that you are interested in the subject, are able to understand concepts of that subject and they will not have to start at zero when teaching you. THAT is the part of it which is important to them and increases your chances. Having acquired that knowledge through simulations of any kind (unless they were official NASA-simulations at a special program for specifically talented high school students) will NOT make a positive difference. Having spent your free time on extensive simulations could mean you have a distorted view of the subject and its contents, maybe even an approach to it that will hinder you in learning it the way it is taught in class. It could also mean that you have wrong expectations of a career in the field and will ultimatively fail because you took the class for the wrong reasons. On top of that comes all the stuff people said before me about videogames. It's a lot better to say you learned all that stuff from a book (preferably even one of a professor who is teaching there) because you loved the subject so much...don't over-do it and don't lie, but if you are interested in the subject one can assume you have also read books about it, yes? So what can you use KSP for? One great option would be to organize your own class/activity at your school where you teach others about space using KSP EDU. You also might be able to get a nice screenshot with a lander on the mun, Kerbin in the background and a flag with the logo of the college on it at the end of your application if it fits thematically (as sort of a creative thing on your app that makes it stick out). Other than that though, leave it out. A spaceflight-college is not specifically looking for students who are interested in spaceflight, it's safe to assume everyone there is Other qualities such as a desire and ability to learn a lot, being able to present yourself, speaking in public and leading as well as social skills and good grades are what makes the difference.