What is the expected duct leakage reduction by have a smoke tested performed and failures repaired and how much will be saved in energy costs?

That would largely depend upon how bad the ducts leaked prior to repairing. If there was initially very little leakage, then the savings/payback for the test would be longer. If the the system was very leaky, the payback would be extremely quick. From our experience, a 30% reduction in leakage can be expected. Remember, the test and remediation is performed prior to air handler, insulation, drywall and register installation and any other factors. Even small duct leakages at a long period of time can be significant.