I decided to "roll my own" and write Python scripts that outputted SVG markup. I was worried this would go about as well as every other "roll your own" project does, but was pleasantly surprised. It is surprisingly easy to output reliable, good-looking SVG graphics using Python. If you are making a chart, everything is just math.
The infinite scalability is almost just a happy upside to the simplicity of creating the visualizations, which is annoying in raster format. It made me like SVG even more.