Spell checking reStructuredText

There's a Sphinx extension for spell checking. It uses enchant, rather than aspell, but perhaps you might find it useful.

https://github.com/sphinx-contrib/spelling

(formerly https://bitbucket.org/dhellmann/sphinxcontrib-spelling)

there's a blog article about it here:

https://doughellmann.com/blog/2011/05/26/creating-a-spelling-checker-for-restructuredtext-documents/

which explains how the extension was created, so if you're set on/stuck with using aspell specifically, maybe you can adapt it to aspell.