[top]Amplify/Dampen Magic
Simple tests would indicate that amplify and dampen magic apply their bonus damage/healing components before coefficients are calculated. Easiest way to verify this is using Arcane Missiles in a duel. Since arcane missiles deals the same damage every time it's cast, we can see the difference between an amped and non-amped target and calculate the coefficient applied. Arcane Missiles was using both the base spell damage coefficient (1.43) added to the Empowered Arcane Missiles talent (.45), and applying that to the bonus spell damage from amplify magic. This assertion can be verified by repeating the test used.
Logically it would be assumed that all other spells would interact with Amplify/Dampen magic in a similar manner. This would mean that an instant attack from a boss would use the .42 spell damage coefficient standard to all instant magic attacks, meaning that only 50 additional damage would be dealt. One would also assume that healing done would be calculated in the same way. Healing spells would have the bonus healing applied in the exact same manner as bonus healing from gear, and would also be affected by coefficient talents such as Empowered Healing and Empowered Rejuvenation.