> The link does nothing because what is directly below the TOC link is the table of contents.

Yes, that's the impression one gets when the link doesn't work.  But the links below are just the sections for the current page rather than the table of contents for the devguide.  Compare, for example, the left column here:

http://docs.python.org/dev/library/argparse.html

The table of contents for the devguide can go on a separate page like it's done for the Python documentation.  We can decide what level of sectioning to display (assuming Sphinx lets you configure that).  Personally, I think I would prefer a shallow TOC (i.e. one or two levels).