I don't believe this is possible in normal view. It is a good suggestion though, either be able to assign a vertical separation for child thoughts, or have a preference to have the thought separation expand to fit. If there are a lot of thoughts vertical separation is reduced, a few, vertical separation is increased to promote readability.
I'm not sure if you asking for your own use or presentations. Several other things you can try are outline mode (may or may not be easier to read), and normal view - Expand All. Normal View - Expand All will show the parent and child thoughts for all thoughts on screen. This will make it busier if there are a lot of child thoughts. However, if you only have one or no child thoughts, the thought spacing will still expand. You may try playing with it and see if it makes things worse or better (unless it's an information dense brain, then it will make it worse). You can also fade distant thoughts in this Preferences > Look and Feel, and control their size in Preferences > Views. Finally, you probably have already tried this, but in case not to reduce the visual clutter of the plex: Use a simple theme with no picture background. I'm partial to my solarized ones, but that's just me... If the active thought indicator is on (Preferences > Look and Feel), turn it off. Turn off Siblings (Preferences > Look and Feel) Play with the link thickness, depending on if you want them very visible, or not. Hopefully you find something of use here.