For element hiding rules I would prefer "edit filter in effect" in the right-click menu of "(open) blockable items [on current page]" to respawn the editor that was used to initially create it. Currently that edit opens "adblock plus preferences" and only allows one to tinker with the per se text of the filter.
This would have allowed me to widen or narrow this filter visually
I don't think this is possible - the composer for element hiding rules needs an element to work on but this element isn't known. Adblock Plus only knows that an element hiding rule was applied in a document but it doesn't know which element it was applied to.
So this leaves us with the (rather common) scenario where the filter belongs to a filter subscription - you probably don't really want to edit it then but disable (and probably also look at the subscription it belongs to). And with the scenario where you want to delete the filter instead of changing it (this can be solved by having "Delete this filter rule" and "Update this filter rule" buttons in the dialog instead of "Add filter rule").
It also doesn't make much sense to have this for element hiding rules only - the first candidate would be the "usual" filter composer which is actually part of Adblock Plus rather than Element Hiding Helper.