It's still not lost near valve-float.The valve spring pushes all the valvegear closed at maximum velocity.The cam slows it up for gentle valve seating.The force pushing on the cam returns that kinetic energy to the cam.Dances with Shrapnel said:Maybe at idle but far from accurate statement as the engine speed increases. To illustrate, take this to an extreme point of just at valve float; most all the energy that goes into opening the valve and is lost.
If the valvegear completely missed the closing ramp and landed on the base circle,things would be different.You could have big problems too.