I agree with the general views in this thread, but feel compelled to comment....
1. To the OP: If there's something that you are genuinely passionate about, and would do it anyway (without the MBA apps on the horizon), then do so. If you're just planning on it for the sake of having some EC on your resume, you're a) doing yourself a dis-service and b) grossly underestimating the ability of the adcoms to see through this ploy.
2. In response to the example of the Indian IT stereotype getting into Wharton: You don't really know if Wharton selected him because of his non-formal leadership role or despite it

All I'm saying is, sure, if you can demonstrate leadership potential without having been in a formal role, that's great (and I'm sure that there are many budding leaders here

), but if you're already been promoted to it, and have gotten there ahead of senior members based on merit and potential, it gives you a solid base for your leadership essay - you have just that little less to prove, and just that little more to set you apart.
And yes, after a brief hiatus, I'm baaaack!!