This is a topic that folks will argue about forever. Clipless pedals are only part of the equation. If you go clipless, then develop an efficient pedaling stroke to go with it, then yes, you will be more efficient (How much more efficient is hotly debated). If you do clipless but keep the same pedaling stroke you have now, then you won't gain much.

You also involve more muscles in your pedaling with an efficient clipless pedal stroke. That's especially advantageous for recumbent riders like me, since we can't change positions and thereby recruit as many different muscles for pedaling as an upright rider can.