The impetus for #handout was exactly guided notes. I think it still aligns with your heuristic of a #handout as something to be passed out to be read, it just has room for students to take notes as well (and then read; they are filling in parts of the stuff to read themselves). A #worksheet is something students use to guide their individual or small group work, via a collection of exercises or project-likes.
Practically, the only difference in current pretext implementation is that an #exercise in a #worksheet has its components controlled separately, since they are "worksheet-exercises," while an #exercise in a #handout is an "inline-exercise" (a checkpoint). One of the side-effects of allowing workspace in more places for #handout is that this can also be done in #worksheet (and I don't see any reason to add a bunch of code to prevent this).
One more thing: Mitch and I chatted the other day about how it would be nice to allow @workspace on elements in a slideshow, since that is very much like guided notes, just using slides instead of full sheets of paper.