I'm really glad you've found your purpose.
Every person goes their own way. Some of us believe that bettering the world is about taking proactive stances on major issues (such as alternative energy). Some of us believe that you better the world by bettering yourself, and the influence of that spirals out of you like a flame and ignites others. And some of us believe that the concept of "bettering the world" is nonsense. In fact, that could be more of that ego that you talked about. The idea that one person thinking that we, as people, are having an effect on the planet itself could be the epitome of ego because the planet is fine.
Things like alternative energy are not bettering the planet. They are bettering our survival as a species.
What is the next step in personal development to me now that I've moved beyond the general topics of personal finance, social relationships, career, etc. and am staring at the edge of examining personal beliefs?
The next step for me is exploration of things that exist outside myself, touching and connecting with those I come into contact with, and finding work that expresses the nature if my life in such a way as it outlives me and touches others lives. Essentially I view the world as a gigantic playground now. And I recognize that my footprint is miniscule in the grand scheme of things, despite the ideas that the things I choose are somehow harming this great planet.