It was easily measurable if you ran the instructions in a loop and looked at the power draw. I can't remember the numbers now but it was definitely significant (maybe 30% on a wide vector instruction?).

I don't know where you got the idea about the flip-flops from.

Adders for example are implemented so that they grow exponentially in the number of bits in size, so that they use a time proportional to the log2 of the number of bits. Note that this means the number of bit transitions in a simple add can be much larger than the number of bits going in, meaning more power draw.

Of course we didn't worry about the instructions inputs in practice.

I think it was cheaper to store 1bits than 0bits ironically.

edit: explain more clearly that larger circuit size means more power drawn