Luangm,
First things first - it may seem like your "perfect plans" have come crashing down, but put things in perspective and realize that you are only 24, and for all practical purposes you are just getting started. Given your age, I do not feel that it was a mistake for you to apply to only "stretch" schools - time is on your side and you have enough of it to rethink your goals and apply again within a few years.
My profile is very similar to yours, identical GMAT, CFA progression, UG etc, and here's the kicker - I applied to Wharton 2 years ago (when I was 24) and received a royal ding. A few years of introspection and corrective measures later, I feel that I now have a stronger profile and clearer sense of my goals (Wharton actually isn't a good fit for me). Here are a few things that I have tried to address over the last two years, it may give you some insight given our similar profiles:
1. A 760 GMAT does not really carry that much weight when one is applying to a Top 10 business-school, even less if the applicant comes from an engineering background since most engineers (i.e your applicant pool) shall tend to have good GMAT quant scores.
2. Taking the CFA exams with an engineering background does show good academic vitality, however once again, in order for this to carry much weight with adcoms, you need to be able to "spin" it beyond just a demonstration of your quantitative ability - your degree and GMAT score already scream that out.
3. As a younger candidate, the adcom is more interested in what you can bring to the table as you sit in an MBA classroom - what leadership skills have you developed? What failures have you experienced and what have you learnt from them? What level of interpersonal skills do you possess? These are the areas that shall differentiate you from all the other "GMAT stars".
4. At 24, I was still very hazy about my career goals. 2 years later, my career direction / goals are more mature (and very different that 2 years ago). Take the time to really think about what you want to do immediately after you MBA.
5. YES! EC is VERY important! Especially with someone with your background. It will prove that you are more than just a glorified calculator, and will add a lot more weight to your application. As far as suggestions, I would say go find something that appeals to you, and do it. Saying that you volunteered at a soup kitchen is OK, but nowhere close to writing about how you discovered a passion and developed it, and how it has developed your personality and profile for business school.
6. Seek out leadership roles. It is understandable that you may not have an opportunity to formally manage people in a professional setting, however leadership goes beyond your job title. Make sure that the next time you apply, you have solid examples of demonstrated leadership.
Applying for 2013 or 2014 is your decision, but I would say that you should take solid steps to address any shortcomings in your profile prior to applying again. And yes, maybe this time consider applying to a couple of safety schools too.