is a good starting point, it would be awesome to be able to see diffs of past changes that are good examples of common development tasks. (By "good" I mean: well-coded, do everything correctly, follow style guidelines, well-commented, etc.)
These diffs could be linked in the development section of the wiki. As an added benefit, this would eliminate the need to write additional developer documentation. That takes time - and the diffs are available right now.
Some example common tasks off the top of my head:
* creating a unit test
* adding a configuration option
* adding a new localization language
* adding new syntax
(I'd do this myself, but I don't have sufficient understanding of DokuWiki's internals.)