AFAICT, there's no hard consensus here; I've seen both patterns, and I haven't seen either pattern disproportionately criticized. As you say, separating distinct thoughts into multiple posts maximizes the potential clarity of feedback provided through voting. In the case of edits, it also causes the new thought to appear in the Recent Comments queue, which some people read; this makes the new thought more visible to those people.
If it's worth saying, but not worth its own post, even in Discussion, it goes here.