How to balance this one?

For a long time my job strategy was to do something helpful. At a time when my best friend was depressed, I wanted to be a psychotherapist. After I started learning my third foreign language, I wanted to work with immigrants to the US. After my first class in the feminist and gender studies department, I wanted to work in a domestic violence shelter. Finally I wanted to travel to other countries and work in microfinance or some other kind of development.

And by now I've come to believe: my labor is not that useful to saving the world. I think the world's worst problems are not in the US, and I as an American am not particularly useful to solving them. Anyway, I seem to have gone through seventeen years of school without studying anything very practical.

So now I'm convinced that my money can actually do more good than my labor. For example, I could join the Peace Corps and spend a year learning a new language and the names of the people in my village, eventually maybe accomplishing some useful work during the second year. Or I could work a job I'm good at in the US and send my earnings to an organization in the village where people who actually know what they're doing can make their own decision about what they need most. (One thing I like about Oxfam is that they do most of their work by funding local partner organizations, rather than sending Americans zipping around the globe trying to fix things.)

There are some problems here:

1) not many people want to do good works, but lots of people want money. The competition for high-paying jobs is a lot higher than for directly useful jobs.

2) The thought of going into business, law, medicine, etc. makes me feel ill.

3) If money rather than work is going to be my primary contribution to the world, I don't know how much is enough. At our current cost of living, Jeff and I can easily get by on my $18,000 salary. (If that sounds low, please note that it's 25 times the median household income in Haiti). But since we keep more or less only what we need, we get no more benefit from a job that earns $80,000 than from one that earns $20,000. And I think most higher-paying jobs would result in me being less happy.

Usually I don't think money is a good goal. I think people are happier if they choose jobs they're good at and that leave them with free time and energy to spend doing other things. I'm distressed at the thought of measuring my life by it. And if I do something I'm actually interested in, like social work, I'm saving my sanity but abandoning people who don't have the basics they need.