Not sure what you mean by 'newer', stretch bolts have been in use since the '80s, Escorts had them.
Never seen a sodium filled intake valve, there would be little reason for such expense (intake valves don't need the cooling, they get cooled by the incoming air). The sodium filled exhaust valves are easy to spot, they have big stems since they are hollow. The real danger is not corrosiveness, but explosiveness. But even regular exhaust valves are high temp alloys, not much good to a smith.