Is there a tool I've overlooked that can quickly compare your edited solid model geometry with the geometry that was first opened, or last saved? 

I know you could save with a new name, open the original, do a geometry compare, then save the new one over the old one when satisfied. That's too much work.

Scenario: 

Open a part, modify some features, compare changes to original to identify any geometry that was not supposed to be changed, before saving.