rsvg-convert 2.40.11 calculates SVG bounds incorrectly resulting in an empty or cropped image. (See my comment in Homebrew repository and the bug report).
Updated @ 11th of May, 2016: how to install the older version (2.40.10) of librsvg on OS X with Homebrew:
brew uninstall --purge librsvg
curl -O https://raw.githubusercontent.com/Homebrew/legacy-homebrew/7a58ff6e07dd35d438193a2e551cf282c2088a44/Library/Formula/librsvg.rb
brew install librsvg.rb
brew pin librsvg
Works well on OS X El Capitan.
Thanks to haio for a correction.
Thanks for sharing, it certainly saved me some frustration!