The neat thing about mysteries is that because there is no resolution, you can rearrange the pieces many times when thinking about it. These "pieces" naturally lend themselves to the flash card metaphor. Using Anki for them means eventually some clue that you haven't included in your current pet theory pops up again to make you rearrange the pieces.
I've also used Anki for workouts: cards per exercise, spaced repetition is normal for training. It's also useful for reinforcing habits.
You can also use it to teach yourself positive thinking or other mental exercises. Use the cards to record general "truths" or positive general statements about you, life, your circumstances, etc.
One unique nicety of this is that it gives a fortune cookie feeling when you draw a card that is especially relevant to your current mindset, and feels more external than inventing a statement knowingly while in a poor state, which makes it feel more impactful.
Really, there are so many things other than rote learning for which Anki is a neat tool!
I also sometimes feel old, but I can ensure both of us: we're only old when we stop learning.
Anki on a mobile phone (with only that as application) is one of the applications I envy current youth about. I really wish I had this back when I went to school, during the commute and breaks. That being said, we did use spaced repetition to learn words.