Science majors are definitely a minority, but they do exist. It's kind of nice that way, actually, because you take all of your classes with the same people and get to know most of the girls in your major over your four years. Chemistry is a lot smaller than biology and neuroscience, so I get the feeling that all the chem majors are like family, and the department treats them as such. With bio, you need to be pretty involved to get that experience (which I am and do).
Despite the minority of science majors, there are a lot of premeds at Barnard. There's been a pretty big shift for medical schools to accept more humanities majors (so their doctors are more "humanistic", which I think is BS but that's another conversation
). I think the reigning pre-health club has over 200 members at the moment, and that's just the people who felt compelled to join a club for it.
As a biology major, I really appreciated the 9 ways. I love science and I love my major, but I also realize the benefits to a liberal arts education and know I won't get the chance to learn much outside of my field once I hit medical school next year. The nice thing about the 9 ways is that you can customize it to include the classes you WANT to take, rather than having to take 15 pre-determined classes. I took classes in economics, anthropology, comp lit, history, and dance and loved all of it. As for how much it takes away from my major.... I'm going to have to say it didn't. I never took more than 16 credits a semester and still felt like I took almost all the classes I wanted to take.
It's funny you mention GPA... almost all the premeds I know consider the science classes the ones that bring down the GPA. I did about as well in my sciences as I did in my 9 ways. A perk to the 9 ways, too, is that you can take them pass/fail for a nice, stress-free learning experience. Barnard allows like 21 pass/fail credits (although a smart premed won't pass/fail more than a couple classes).