In my humble opinion, sticky threads should only be related to forum rules and important announcements from the management. They should include “frequently asked questions” about various aspects of forum so new users (and users returning after a long time) can easily orient themselves.
By making any other thread sticky, a sense of higher value is attached to that topic, which may or may not be interesting to most readers.
If the majority of readers/posters value certain threads greatly, surely one of the poster will bump it up the list if it starts dropping down.
Just a thought…