Thought from the inside:
As an SOP Admin, I wouldn't tell you to leave out any activity to which you were seriously part of. Your ECs are part of who you are.
Also, you never know what might resonate with a reader. I had a friend in grad school who was in law school, right in the middle of the class academically, who was applying for clerking internships. The ONLY reason that he got an interview (and ending up with a clerking job) was because he listed on his resume that he was a licensed stuntman, a certification he earned because of theatre roles he had played. The partner at the firm who was in charge of internships was curious and wanted to meet a stuntman. He got his foot in the door, then talked his way into a position.
The moral: you never know what interests of your will catch the curiosity of someone on the other side of the decision-making process.
Eric H. Hobson, Ph.D.
Assoc. Dean
Belmont USOP