Competing in Battlecode was one of the best things I've ever done. Yes, it's great experience. Yes, you'll become a better programmer. Yes, it's a lot of fun.
But you learn things about yourself. Battlecode was my first love. It was the first code I wrote that I really poured myself into. The hunger for victory, the desire for perfection, the frantic last-minute hacks and patches...a lot of emotion goes into this competition, and I was not expecting that. I was an unmotivated, procrastinating slacker in high school. After doing Battlecode I saw what I had in me. I saw that I really could work, and work hard. I could work hard and love it! That has been life-changing for me.
I cannot recommend this competition enough. Participate, put everything you have into it, and Battlecode will give back.