Other than faster engine warmup WAI are a waste of time for fuel savings. They just increase energy lost to the cooling system and increase polution.
Ram air on a gasoline engine are of no use for fuel savings. They can provide a small bump in power though. On a diesel they will provide a benefit in both power and performance.
At sealevel 70 degrees F and 70mph you can get a theoretical maximum of 0.09 psi of boost.
Ram Air Calculator