If you tilted the wings as well as the engine to a more downward angle on a plane, the plane wouldn't function well because its center of gravity will be disturbed. The position of the center of gravity affects the stability of the airplane, and the placement of its different parts revolves around the CoG. Learn more about an airplane's weight as well as its balance at http://www.pilotfriend.com/training/flight_training/wt_bal.htm.
No ... think about it. They run computer and wind-tunnel simulations all the time, especially before building a new plane design. If they could have come up with a change to make for faster takeoff/climbing - they would have already done it (to save on fuel costs).