Hmm, that is a tricky one. I don’t think it’s possible to get the surface area of an AutoCAD Body, either in Dynamo or not. You could explode them all down, but then you will probably get a mixed bag of Regions and Surfaces, so it’d be more tricky to handle all of the different potential object types.
One approach could be to use the LINEWORKSHRINKWRAP command to generate a polyline along the boundary of the bodies, but that would be a 2D area and not a true 3D surface area. That could add up to a significant difference with large areas.
What about ignoring the AutoCAD Bodies altogether and doing the computation directly with Dynamo Surfaces? You could create lines connecting the desired point/link codes and then create surfaces with Surface.ByRuledLoft. Something like this:
I guess from there you’d have to assign the values to a Property Set or something in order to get them into Navisworks.