Usually I don't consider these things to be of common interest for a Telvanni, but in this case I'll have to make an exception. I discovered an addon called "Screenshot Helper", that ensures that the "hide UI" button you can configure in your key bindings does its job instead of stopping halfway through. This hides group and quest indicators as well! I've been looking for this for ages and couldn't bear the thought of you continuing your adventures without knowing of this magnificent tool.
A complete list of my addons can be found here, in the public section of the forum to share a bit of our research with the common people.