Not perfect but if you double-click on a node it will show you the control and deviceId it's currently mapped to. The internal deviceId tends to be cryptic though.
As far as mapping multiple physical knobs to real knobs, I would tend to think "that's a feature", but it would be possible to add a warning.
Definitely agree that it's a feature that should be allowed, but forgetting how many knobs you've already used and reusing one so it's attached to two different things is ... pretty confusing when it happens. :D
It's could be just drawing the paths on top of the nodes in this special case would do the trick, but it seems like it could come out better if it's actually represented as a single orange-outlined rectangle that's filled with the path color, so it's consistent-looking even if the node alignment isn't perfect.
I thought you said being able to map multiple physical knobs to the same virtual knob, but I actually found that there was a bug last night. Normally a single virtual knob should only map to one physical knob. This is fixed now! :)
Regarding your comment on component reuse via grouping, it would be cool to be able to select a set of connected nodes and call that a “functional group” which you name and also specify named inputs and outputs to it which get wired to specific inputs or outputs on nodes in the group. Then have the name you gave it be one of the node types you can build with on the “add mode” list.
As far as mapping multiple physical knobs to real knobs, I would tend to think "that's a feature", but it would be possible to add a warning.