a-concerned-mother

Probably the most simple examples for me are

1. Showing the multitude of packages for something like an email client, Margit, etc and how you can mix them together with org linking, using babel, etc. showing the deep level of integration you get

2. Simply show functionality in the editor and how you would like it to change. Rather that writing a whole package to do it. Use the help to go to the source and redefine that function in your config. Doesn't require them to know elisp to understand but it gets the point across that everything is at your fingertips.

If you prefer a more modern looking interface there is also https://emacsdocs.org/docs/elisp/Emacs-Lisp

I can personally say yes ... yes it is everything you learn has a use case and can be applied everywhere in emacs and in other languages