I would define RestoMod as a car that looks stock at first glance but has some cleverly hidden upgrades.
Examples would be:
11.75" brakes (most people wouldn't even notice they are larger)
Aluminum heads cast to look like stock and painted the OEM color.
Painted aluminum intake
Stroker motors running cast iron manifolds
5 speed swap with a stock handle so the interior still looks OEM (at a glance)
FiTech or Snyper hidden under a stock air cleaner
I see no real relationship between pro-touring and restomod, nor the parade queens as referenced above. To me, they are all different beasts.
Finally, I would define pro-touring as a car with modern upgrades to maximize the handling and driveability, often at the expense of originality. Big brakes, wide/lower profile/sticky tires, stiffer springs/shocks, chassis stiffening, etc. This isn't limited (IMO) to just the chassis, but could include more power and some creature comforts (AC, CC, etc.). Maybe the best definition would be "a more modern classic".
Just some thoughts.