I'll respond based upon what I think this thread is asking or suggesting.
You'd like to see a place where there is a library of useful expressions and some discussion on how they work. And your suggestion is a single sticky thread on Interact.
The wiki is a perfect place for that, and there are some already there. In fact, there are expressions for various needs throughout the wiki and Interact.
I personally believe stickied threads should be reserved for only the most urgent and paramount of information. Expressions, as fun as they are, don't meet that criteria.
The problem with the request is that is assumes others should spend the time and energy to go find all those items, collect them, enter them into a cohesive document, and provide the necessary commentary.
I'll suggest that the amount of work it takes far exceeds the small amount of time it takes to do some searching of the wiki, or Interact, and therefore has marginal returns. And it is very clear from my own experience writing documentation for others that those who ask for it rarely have the interest or ability to contribute. So to me, these requests are tantamount to "I want someone else to make my life easier". I think we all want that.