Out of the many ways there are to boost brainpower, writing is definitely one of them:
1. By writing something down, you are seeing it from a different perspective. If you see it from a different perspective, it means that something has changed in the mind: and this change is simply the accumulation and creation of new neuronal connections.
2. Writing something down also imprints it at the level of beliefs, so that not only do you understand what you are writing down, but you begin to believe it as well. This belief allows you to understand what you are writing with even more insight.
3. When you right something down, it becomes more organised in your brain. This organisation is through prioritisation. So when you write it down, you have prioritised it over non-written things, creating mental organisation.
The other point to mention is that there is a right and wrong ways to write things down. For example
a) To simply write down what others have written themselves is of no use, unless you re-write it in your own words.
b) To write down without paying conscious attention, also is of no use because your mind is simply on the autopilot muscle process of writing, which does not necessarily equate to understanding.
c) Finally, writing something down which you yourself have created out of nothing, is the most valuable, because it is 100% your original content, and therefore the neuronal connections are being forged from the deeper root which lies within you.
What To Expect/Conclusion
Writing is an awesome way to increase your brainpower. It increases specialisation and idea generation. One should endeavour to write and formulate ideas on a regular basis.