Hey Gökhan -- thanks for working on this. We are very happy to have documentation contributions. I don't feel strongly about how the pyplot rst file is generated, whether by extending Sphinx, using a script, or simply hand editing it. I'm actually incline toward the latter, because it would probably be nice to have some simple description in the section header, eg::
acorr - autocorrelation plots
as we do on the main page. Part of the sphinx philosophy is that "hand edited" documentation cannot be fully replaced by autogenerated documentaiton, and this may be a reasonable place to do some hand editing.
If you go this route, update the pyplot module, the developer's guide and the boilerplate.py script (it lives besides setup.py and is a script to generate part of pyplot) so that when developers add a new function to pyplot they know to update the api docs as well.
You may want to move further discussion over to the developers list. Any changes you want to make should be posted as an svn diff to the developers list. If you don't get immediate attention, also post it as a patch to the sourceforge site, and reply to the developers list with a link to the patch -- see