Contrary to the myth of clip-in (and clips and straps pedals before them) even pro cyclists struggle to 'lift' the rising pedal. The best that can be acheived in practice is a slight reduction in the weight of the rising leg, which gives the falling leg less to do. There is a slight benefit at the bottom of the stroke, an ability to claw the pedal back which allows for a longer power stroke. It's easier to 'pedal in circles', the stroke becomes less of an up/down treadle action. Clip-ins allow you to spin faster, and more spinny = more aerobic. The real benefit of clips and clip-in pedals is that they reduce the amount of energy required to keep the foot on the pedal, automatically align the foot in the optimal location and prevent the foot from slipping off.
The limit to the amount of power we can deliver to the pedals is limited by our ability to process oxygen. Even if we could pull up on the pedals at every stroke, it wouldn't be free energy. Clip-in pedals just allow us to be more efficient.