I'm currently using this in my workflow to get all my JS and CSS files from my HTML and then concat and minify them (it's awesome!). There is a problem however, with CSS like Bootstrap. It uses @font-face and references fonts, when I concat the CSS, the paths are of course broken. There are plugins to rework the paths, but no plugin that actually let's me get the referenced files to copy them over to my build directory. Maybe you could make a similar plugin that parses CSS files and returns all referenced url()s, or point me in the right direction on how to write such a plugin, since I have no idea how to approach this.