The non fun answer to this is,
We are not just using 10% of our brain. And that different parts of our brain are used for different functions.
Using 100% of our brain we would be laughing, crying, angry, moving everything uncontrollably.
So lets just say we took a drug that could increase your thinking and reaction brain power 10 fold.
Many games may become less fun, but more difficult games would become more enjoyable I guess. I'd probably use that brainpower for gambling, investing to the point where I wouldn't have to work. Then selfishly put that money towards various projects iron man style and women