There is a technique for putting Veil on plates and headlights which I have found to be foolproof when it comes to looking good. Instead of the normal brush on or air brush methods (I've done both), do the following:
Use an included Veil brush to apply a coat. Take a dry Veil sponge brush and start pulling off all the excess Veil (drip it back into the can) repeatedly until you have a completely even, very thin coat. You may need 2-3 dry brushes to do it right depending on how much area you have to cover so make sure you have spare brushes in advance of application.
It will be damn near perfect this way, but too thin for use. Keep at it, it will work and isn't near the "perfect" stage until its very thin and tacky. Once its how you like it, let it dry overnight. Repeat the procedure a 2nd time and it should now be thick enough to be effective. It'll slightly darken tags and make headlights look tinted.
No more splotches and runs from a standard application, and no more specked look from an air-brush application. This type of application results in an even coat. In a test with one side of a tag Veiled this way, and the other side clean you can't even feel the transition point with your fingers.