What I do need sometimes is a sounding board for where a plot may be going. Sometimes, this is a matter of how to resolve a particular subplot. In other cases, where the writing is at least to some extent do-over/what-if/autobiographical, I'd like feedback on plausibility, maybe offering some explanation.
LughiIldanach, I've got two points to your question. First of all, the need for a structural editor is quite different in non-fiction and fiction. But, in answer to your question, what you really need is author feedback. I like to keep the emails of a couple authors that I trust. If I run into problematic chapter, where I'm unsure about something, I'll send them a single chapter to review for me.
Authors are more focused on things like pacing, foreshadowing and consistency, and are more willing to suggest alternatives than editors will.
Most authors on this site will likely help out (assuming you stick to the 'one-chapter rule' and don't overwhelm them). They key is to find a couple who share a similar writing style and who you respect.