Nearly all, or I might as well just say all - conventional oils leave a slimy film, residue, or some form of gunk on internals. If synthetic (at least a good synthetic), the parts appear "new" with a slight brown coating of what would look like fresh oil. The exception might be diesel conventional oil.
Not really. I pulled the valve cover off my old '88 Accord after 270,000 miles running conventional oil. It looked pretty darn clean. No deposits. No dirt.
I've seen the head and bottom end pulled apart on a neighbor's '86 CRX with over 200,000 miles... same story.
I've run conventional Pennzoil since I started driving. I've never had any internal failures. No leaks or oil consumption, either. On the motor I pulled apart (stuck thermostat caused overheating, which cooked the valve cover gasket), there was no engine wear. Maybe I'm just used to Hondas, which do wear better than most (if not all) other engines.