I would argue that your admission to Wharton is dependent on more than just test scores/GPA and a demonstrated interest in finance/business.
True, the first two items are virtually a necessity, and the third is nice to have, but if the most you can offer for why you want to study business/finance at Wharton is that it interests you (and the implicit reason of “I can make a lot of money”), you probably aren’t going to get in.
The best item that you can show to the admissions committee is not only a demonstrated interest in business, but a concept of using the knowledge that you will gain from Wharton towards a social good (e.g. microfinance in your case). Remember that the course of study you give them is only tentative, and it’s expected that your goals will change. As such, as the top undergraduate business school in the world, they aren’t really admitting you on being interested in business, but on what you perceive the value of a business education to be.
As such, take a rigorous courseload, have a good GPA, and get a good SAT/ACT score. That will help you anywhere, even if you aren’t admitted into Wharton. However, if you want an excellent shot for Wharton, I would suggest the “finance club” idea, and a lot of community service. Penn is a school that values service and engagement in general, and having this on your application will make you a synthesized applicant who is interested in business for more than gaining money (and trust, distinguished applicants who have started finance clubs really aren’t that hard to come by in Wharton’s applicant pool).
Therefore, the key to getting into Wharton is the usual academics, some interest in business/finance (even though this isn’t an absolute necessity), and giving a business education a sense of purpose.
I won’t say that I’m an expert on getting into an Ivy League school. However, considering that Dean Furda could partially remember what I talked about in my “Why Penn?” essay, I can offer you some advice from that vantage point.
Ultimately, an applicant who wants to study business for no reason than making money (even if they appear to be a decent business student, but not extraordinary) isn’t really a likable person, or a compelling case for admission. Assuming that they have no hooks, they’d probably be a “maybe if we have room” type of candidate. The distinguished applicant who has the usual and that somewhat lofty but well-developed sense of purpose would be strong, even without hooks.