I have no analysis to back it up, but my gut feel agrees with Andrew R Stewart's post #34 . I.e., by the time the spokes are loose enough to result in significant energy loss, you're facing other, more immediate problems, notably high risk of tacoing a wheel.
The situation you want and is the design intent of a spoke wheel is that the static tension is high enough that the variable tension due to load reversal on rotation is a reasonably small fraction of the static tension, (and preferably less than 20% of the UTS so that we are within steel's fatigue limit, i.e., assuming steel spokes).
But unless variable tension is approaching 100% of static tension, I see no great absorption of energy through this mechanism.