One thing that has led to me creating way more highlights is KOReader+BookOrbit. Now that I know my highlights aren't locked up in Amazon/Kindle's ecosystem I'm more likely to highlight something.

I had a lot of fun hooking up some e-ink displays in my house to call out to BookOrbit to get the highlights and display them. Highlighting something in my book and then seeing it on a screen a day or two later is more fun than I would have guessed.