Von Neumann for example was incredibly brilliant, yet his brain presumably ran on roughly the same power budget as anyone else's. I mean, did he have to eat mountains of food to fuel those thoughts? ;)
So it looks like massive gains in intelligence or capability might not require proportionally massive increases in fundamental inputs at least at the highest levels of intelligence a human can reach, and if that's true for the human brain why not for other architecture of intelligence.
P.S. It's funny, I was talking about something along the lines of what you said with a friend just a few minutes before reading your comment so when I saw it I felt that I had to comment :)