If interviews are involved in admissions (or awarding of scholarships) it can help. Also, as ZenScanner suggests, I do think a polymath will look different on paper than the student with a long list of organization memberships that only demonstrate superficial involvement.

I will say that as a faculty member in an arts/humanities area, my favorite students have been the very intelligent ones with strong and often unique interests beyond my own field. Often this will be a student with a science major, but also a real love for art/literature, or sometimes it is a student engaged in 2 or 3 very distinct areas of the humanities. Can't say these are typical students, but I'm always happy when they turn up!