Craig, the salt in acrobatic dough, the kind you see in competitions, is a different animal than the salt in regular dough. In that instance, the inedibly high salt content makes it easier to spin/stretch without tearing. For regular NY style pizza, though, salt is predominantly just for flavor and plays no role in stretchability.
Stretching boils down to 3 things.
1. A properly formulated and well fermented dough. If you're aware of the protein content of the flour, use the right amount of water for that protein level, knead the dough the right amount of time (not too much, not too little), and are aware of your yeast activity and the factors that increase it and decrease it so that the dough can be ready when you need it... you will have a dough that will practically stretch itself.
2. Good stretching practices. Pressing the dough out with your fingertips, leaving a little extra mound in the middle, forming the rim, stretching the edge, knuckling stretching and avoiding the center- if you do each of these right, it makes a really thin stretch far easier.
3. Practice. There's a feel for stretching dough that can't be taught. You just have to stretch a lot of pizzas and you pick it up. By the time you hit 20 pies, I think you'll start to recognize the hand movements that stretch the dough thin, but not too thin. If you can open a pizzeria and make thousands of pizzas like Paul has, that helps