Will having an ACT/SAT score help my chances of getting selected for MECEP?

I submitted on last years board with a relatively high asvab and a 1050 sat. That was only 50 points higher than the minimum and it was from when I was in high school. As long as your asvab is high and the rest of your package looks good, then don't worry about it. I only submitted both because I had them.

It helps to have test scores well above minimum standards. It would probably help more to have some college classes under your belt with a high GPA. I am presenting what I had in my package that worked for me. I can't say that they look for the same things year to year as it depends on the board reviewing the packages.

I was in MECEP '86. Was selected on the first try. I had no waivers but if I hadn't made it I would have needed an age waiver the following year and waivers decrease the chances of your getting selected.
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My SAT was 1230 which is good but some of the other MECEPs had higher. Most had scores above 1100 if memory serves correct. What I believe helped me was that I had taken almost a full year of college and had all A's and one B. In addition to that I was a 300 PFT'er and shot expert. The letter you write explaining why you want to become a Marine Officer must be well-written and grammatically correct. You must be able to communicate well in written correspondence. As an officer you will be writing a lot of fitreps, awards, and corresponding as liaison with other units, service branches, and gov't agencies. You must look good in uniform and your duty assignments and endorsements also factor. Demonstrated combat experience is a plus. Leadership billets such as fire team leader and squad leader will strengthen your package. I had two meritorious promotions but no combat experience. At the time I was selected was an Avionics instructor. My fitreps were strong but I wasn't the highest rated Marine Sergeant in the group of Sergeants that was ranked on my fitrep.

I believe it was a combination of strong written letter stating why I wanted to be a MECEP, along with demonstrating that I was able to handle college. The 300 PFT and Rifle Expert were just the icing on the cake. If you have a PFT 285 or above, that's plenty good. You will be competitive with those who run a 300 PFT. How high your Rifle Expert score is doesn't really matter... so long as you consistently shoot Expert.

Well, hope this will help you gauge what makes for a strong package and help identify any areas needing more work before you submit.

If you don't make the board don't let that deter you. If your commands keep recommending you that says a lot and your chances of getting selected will go up -- especially if your package is stronger with each subsequent submission. It will show the Board that you are serious and dedicated to imroving yourself in order to achieve your goals.