I hope I express this well - forgive me if I don't - but sometimes I wonder if people have a problem with the seeming lack of day-to-day structure or prioritization in GTD because of cultural influences.
When I read or listen to DA, his approach seems to be more Eastern, while many of us were surrounded by and continue to be influenced by Western thought - which says you must always have a plan, an outline, a schedule, a map, a hierarchy.
Not that GTD is totally stream-of-consciousness, there is a lot of organization there (particularly in becoming aware of all the commitments - "agreements" - you have out there), but it seems like, at a point, DA is telling us to "use the Force", trust our intuition - deep down we all know what's important and what's possible right now. And though setting it down "in stone" (or at least clay) for a day or a week at a time may make us feel better when we make the plan - it ignores the fact that, though "the plan" is completely under our control, Reality is not, and events will almost always force us to alter those plans (or scrap them completely).
I am trying to become more comfortable with what (it seems to me) DA recommends - if it must be done on a particular day - then it goes on the hard landscape. If not, it goes on an unscheduled, unprioritized, contextual list. My comfort with this method fluctuates from day-to-day, but I suspect it's that clash of cultural differences from my upbringing that creates much of the discomfort.