( but I have to say that the insight which it gave me into the pattern of what OF (reveals | conceals | decorates) became a factor in my moving away from OmniFocus )
I used the Rob Trew script to move it into a mind map for a while, but gave up on it a while ago.
I agree with the OP though, a built-in visualisation tool would be great. Surely Omni could leverage some of their OmniGraffle technologies to give us something that looks great and is fully integrated.