One annoying thing when adjusting spacing is when the selection isn’t left aligned.
The way it is now is if you have a group that is positioned to the right in a frame, and you change the spacing to that group, you now have to drag the group to the left/right by the total amount of pixels that you increased/decreased the spacing multiplied by the amount of items in the group (minus one).
Since you can highlight objects in a selection, I suggest you should be able to use this as a pivot with which spacing adjusts to accordingly.
Hopefully this GIF explains it:
The gif demonstrates with the pivot at the center object, but you should be able to do it against any object in the selection.
What do you think?