Agreed taking apart the pump is a wise thing to do. Its not difficult and it gives you visual evidence of what's going on inside the pump. I know from personal experience that an oil pump can ingest bearing material, spit it out and still feel nice and smooth to the feel test of spinning it by hand.
Spun bearing sets off deafening alarm bells in my mind. No way i'd ever consider putting the same pump back in an engine that had a spun bearing, w/out at least taking it apart for inspection.
Agreed with Chris on disassembly. Keep the gerotors/impellers marked so you can reassemble exactly as they came apart. Reason being is that the same teeth are always meshing with each other. If you use a paint pen to put a dot on opposing teeth of each gerotor, you'll see the dots always come together as the pump rotates 360 degrees. Also don't mix up the gerotor stack.
Here's a picture inside of my now wall art 964 pump that gobbled up a bunch of bearing debris. Spun just fine by hand. Not even the smallest hint of dragging or roughness.
That said, an oil pump test rig with an old case sounds like a great way to do the flow testing. Still, it's not a bad idea to look inside and see why the flow may not be up to snuff.