I only mentioned serving a mission in my PS as a way to explain how I speak Spanish fluently, I did not count it for any service hours. Here's why (just my opinion) - 1) There's enormous pressure to serve a mission from church leaders, family, and girlfriends that push young men to go on missions. and the majority wouldn't have gone without that pressure 2) The absolute first and foremost purpose of a mission is to baptize/proselytize, and a very small amount of time during the mission is actually used for service, and most service is only done to accomplish the first purpose, baptize.
I strongly felt that I should be able to accumulated enough service/leadership experience independent of my mission, while taking classes and working during undergrad to be a competitive applicant.
That being said, here's what I've heard from various schools - Stan from UoP presented at my school and said basically, we see LDS missions on the apps of basically every Utah app, we don't think it sets you apart, we know that basically all of you do, we need to see stuff outside of that. Brian from Marquette present at my school and said - we like seeing that you guys did a mission on your apps, to us it show that that kind of stuff is part of your nature and who you are.
I had one friend who interviewed at Michigan State and the interviewer straight up asked if his mission was primarily a proselytizing mission or a service mission.
In conclusion, generally it will either do nothing for you or help you from what I've seen, although there may be adcom members who take issue with past controversies with the church and it's political involvements, so that might hurt you if that's the case. Idk....
Sorry, this is a pretty long winded response, hope it helps in some way!