Hovering over a wiring node with the Wiring Tool should highlight what that node is connected to, and when you have a node selected the valid nodes it can be connected to should be highlighted, to help people get out of situations like this:
I think it might be a good start to only show connections with a specific node - and hide all others - when hovering over it. I don't think any amount of highlighting would improve your situation with a mess like that in the above picture. When I need to work on densely connected circuits I usually turn off the wiring tool to think and find the right target, simply because all these connections make it difficult to concentrate.
