Through away the rst stuff and use DokuWiki syntax. Simple, fast and consistent solution for the wiki.
Yeah, if it's not a problem for some users not to use the same thing than Geany use for it's own doc (why Wiki user would even know? :D) I think it's definitely cleaner.
Agree, use wiki markup for wiki, document markup for document, don't use a screwdriver as a hammer, even if it might work some of the time :-)
Cheers Lex