Thats a theoretical question.

Point is, writing down a very large part of what goes on in your mind, and then being able to mine it for stuff can be worked upon.

I find the idea very interesting. I end up ignoring a lot of thoughts that come to my mind, and I usually get most of the ideas when I'm not working very hard. Probably it would be great to take 10 days off work, do nothing, and just write down whatever comes to mind. I'm going to try this.

Right on. If someone really wrote everything that crossed its mind, that person would end up in some kind of infinite feedback loop:

"I'm tired writing." (write it down) "Ok, now I gotta stop writing." (write it down) "I wish I could stop thinking so I could stop writing." (write it down) "Ok, I'm stopping now." (write it down) "Let's try to do something impulsive next time without thinking." (write it down) "Yea, it worked! I stopped thinking... Oh sh..." (write it down), etc.

You have a point. It's the Heisenberg principle at play here. By making the observation, you change what you are observing.

It's turtles all the way down.