I don't think it works that way.

While in general efficient programs can save energy, the "saved" MB/s do not necessarily correlate with saved J. There is no direct cost for a instruction, there is a severe overhead from the machine plainly being switched on. And it's not like you will always be able to "use" that saved MB/s for something else.

And you entirely neglect the "cost" of optimizing. Alone the time spent looking at inefficient code probably cost more energy than all the actually saved energy by a single change.

Consider the time someone could have spent on something else, with significantly more impact.