The advantage of Nelson plugs has to do with detonation and pre ignition at high nitro precentages, because of the smoother surface and transition.  There will be little to no advantage on lower nitro engines, and no advantage due to fuel and air between the threads.  The copper washer is there for a reason.

Also the rolled threads are very precise and more desireable.  If your die is cutting substantial metal off it is because you tend to push the die into the thread.