I find that speed is really the only advantage to spraying. To get a long lasting quality exterior finish requires some kind of hand work. Most of the guys up here use a method called "Back Brushing". One person sprays while several go behind with brushes and rollers and work the finish into the surface.
All surfaces, no matter how much sanding you do, will have a texture to them. It may be a microscopic texture, but it's a texture nontheless. Spraying applies a finish a certain number of mills thick over this texture, but it doesn't reach into the texture of that surface. This leaves uncoated areas of air under the finish that will help in the future demise of the finish.