When scaling up to a real example, the diagram often looks like the inside of a box of wires - lines going in all directions.

Part of this is probably due to VPLs not exposing the right abstractions--and of course, exposing an abstraction organically in a visual representation may be unfeasible. I looked at some instances of LabView programs linked in another comment, and there seemed to be a lot of repetition which would no-doubt be abstracted away in a text-based language.