Thanks Casey. You're absolutely right that it is still very difficult to make retail impact investments. Unless you're able to invest pretty large sums of money then most social enterprises or impact funds won't be open to you. Hopefully this will change soon as the sector develops. But for the moment you may be able to "invest" in some social enterprises on one of the crowdfunding websites. Kiva.org is also a decent option. And at least here in the UK, many community-based projects are open to investors. Check out 5yj.co.uk for example (of which I'm a director).
In terms of how I think about the question of where to invest your money, I'm currently working on putting this question into a more detailed framework. But my intuition is that a mix of impact investments, conventional investments, and philanthropy is the right way to go. But also that a good impact investment will have more impact in the long-run than both philanthropy (because you grow your investment and can re-invest it) and conventional investments (because your impact investment actually has impact).