GTD is a productivity methodology, i.e., with the emphasis on producing stuff. Being contemplative is a different mindset, and it has its value, too; but GTD is action-oriented.
Somewhere DA said that you should avoid having one thought more than once unless you want to. I can relate to what you say, the thinking process in itself has its value too. But from a point of view of efficiency, you want to use that 'computer time' for a different item each time.
I'm not sure, but maybe the thing is that the first GTD book was mostly business-oriented (no loitering in there), and then, only when it became so popular it spread to life in general. At least, in my country (Spain) it was published in a collection of business-oriented books...
(Just my 2 cents...)