When I started, VimWiki syntax was better supported than markdown. I've seen lots of markdown related pull requests come through, so maybe that's changed.
I use VimWiki for:
* Life goals (stretch and short term). I use it almost as a centering tool.
* Passages from books
* Book summaries (that I write)
* Lecture/Speech notes
* Notes on misc. items I want to explore
* Ideas for future science fiction short stories
Beware, highly experimental, and the documentation is lacking (reading the tests would be the best idea to get a feeling how the syntax works).