Campus visits and info sessions can be useful for your own knowledge and research - it's not about putting in face time. If you have the opportunity, do it, but if you don't it's not essential.
Keep in mind that people who are at these top schools aren't there because they spent a year trying to manufacture a profile that would be competitive for these schools. They got in because they had a consistent level of achievement throughout their life - and the b-school thing was an opportunity, not a *reason* for their career/extracurricular choices.
If you want to take a year to work at an NGO, do it because you believe in it, irrespective of your b-school plans. Don't do it because you think it will get you into b-school.
Adcoms like anyone admire highly accomplished people who are internally and independently motivated - and not those whose choices are dictated by gaining validation from others (parents, peers, colleagues, adcoms, etc.).
I recognize that this may be a bit abstract and cerebral - but there isn't some paint-by-numbers bullet point plan to make yourself competitive for b-school. Moreover, that's not what your career/life choices should be about.