I checked out PopChar, and it looks very good!
Are you now satisfied with using EmEditor with PopChar, or are you still looking for a Unicode insert plug-in?
I’m pretty happy with PopChar and I even use it on OS X which already has a really good character palette.
As I use EmEditor for more and more of my general writing under Windows what I would really love to have would be a good inline spell-checker to get away from modal dialogs that get in the way.