Making Django development server faster at serving static media
Consider using mod_wsgi
instead, and having httpd handle the static media.
Development server is simple unsafe single-threaded application, so you cannot do much.
One trick you could try is to redirect /site_media to second development server, but this is ugly and probably wouldn't help that much. So you could try bundling/compressing multiple assets into one css/js (e.g. using YUI Compressor).
And in any case, you should have separate static media server, that can serve multiple assets at once.