Do egg whites thin out when salt is added, which will make them easier to mix? Does adding salt to eggs cause the white to thin out and increase in size, making it easier to mix?
Salt, sodium chloride, is slightly chaotropic towards protein colloids, so it should loosen up the egg whites slightly by decreasing protein-protein interaction.

That should make the whites easier to mix, but I doubt you'll get a significant size increase out of it.