MoinMoin would miss quite some features without the help of some of its users/developers. What you can do to improve MoinMoin, also for your own benefit:
develop new extensions like macros, actions, processors and parsers (MoinMoinExtensions)
run the development version and help testing the new features or test MoinMoin on a certain platform, or with certain Python versions (MoinMoinTesting)
help with the translation efforts, especially adding new languages (MoinDev/Translation)
help developping new themes, styles and icons (MoinDev/ThemeDevelopment)
- etc.
If you want to help you should look on existing bugs at MoinMoinBugs and look what user want at FeatureRequests.
More information on MoinMoin source code and other developer issues can be found in the MoinMoin main wiki, on MoinDev and its subpages.
Contributions
See MoinMoinExtensions.