Looking to find a repeatable way to measure only the exposed area of a large assembly with 1000's of surfaces to find a more accurate area to estimate paint, I've tried a shrinkwrap but that gives the measurement of everything it looks like still, as it keeps all the surfaces of each part, and clicking each surface separately only allows 40 surfaces to be picked at each time
Without seeing the geometry I would use the projected area of the assembly model. This will get you an estimate that is fast and can be set up to be parametric.
By using the 6 planes of orthographic projection, less if for instance the bottom does not get paint.
Try using the projected area functionality in the measure tool. This does have some limitations that the shape can affect.
Projected area of a surface Also done by a numerical integration, but the integral is different from regular surface area in that the projection direction is accounted for This computation is again very accurate, but has a major limitation : the surface being measured must project one-to-one to the projection plane meaning that the surface cannot "double back" on itself when viewed in the projection direction
If that does not work you can manually employ the same approach with features.
Project the outline of the silhouette of the assembly on to planes for each "face" that will receive paint as curves.
Create a fill surface using the projected curve.
Measure the area of each fill surface and add them together
Maybe do a merge part? You could use the boolean functions to make a new part, or export as a solid shrinkwrap. A solid shrinkwrap should not keep non-exposed surfaces, as they are merged into whatever surface they are attached to.