In the User section, before the “bug report” how about “Where to go for help” which lists the forum, IRC and other ways to connect with other Gramps users. This may help steer users to the community before filing bug reports on functionality they might still be unfamiliar with.
“Programmer References” suggest calling it “Developer References” ✓ to include artists, triagers, translators, writers and others who help develop Gramps.
Developer Portal ✓ is one of my go-to pages. Consider making that the first link in the developer section.
The wiki page is a bit more positive. (It assumes people are there to get help from the community, while the WordPress assumption is that they want to report Bugs.) Maybe this could be the “Where to go for help”?
Note that there are extensions to embed MediaWiki content in WordPress pages too. I don’t know if the extra complexity/fragility would be worth the effort. But it might be a way to keep the WordPress content fresher & multi- cultural. It IS the first content that potential new users will see.
The content is very similar and to make the choice simple, wiki is a good choice because of the reasons you laid out and several of the other links are pointing to the wiki anyway.
For both Contacts pages you mentioned, it would be really helpful to first direct Gramps users to any form of self-help, i.e. wiki, forums and mailing lists by moving those section up so users search the wiki/forum first. With limited number of triagers and developers, it would be better to have them spend their time on issues that are clearly bugs or feature enhancements.