Great post and fabulous suggestions.
To echo your suggestions, one strategy I've tried with success is periodic "SOS" posts when we have a larger number of answered posts than usual (typically when the facebook group is busier than usual, and posts just get missed). It looks like this:
^^ The image is a gif that moves, so it's eye-catching and makes people pause. Organization is a huge pain point for our group, so our members love any effort to categorize things.
Just saying great article, awesome suggestions, that stuff really works!