OK, the flat plate would only work until flow separation (ie stall), so it is restricted to a low angle of attack.
The spoiler or speed brake works because it causes drag. It has to be close to 90 degrees to the airflow to do this. It matters not where it is located; on top or bottom of the wing or the fuselage. If it is on top and moves only a little bit it is a spoiler, and works by disrupting the airflow, and causing, again, drag. The 747 spoiler is restricted in range in flight for example. In flight it operates as a spoiler and on the ground as a speed brake. By spoiling the flow it also reduces the lift produced, since a clean flow is needed to set up the whole lift thingy (technical term).
Kermode Chapter 3 has a lot of stuff in it and most is above my head, I admit. But I agree with the circulation theory and it says you need wingtip vortices to have lift. Without them you have just drag. If you have an infinite wing then the CL is reduced because the correction for aspect ratio is to divide the CL by Pi.A (A being aspect ratio). If A is infinite then CL is zero. The discussion is in the book to cover induced drag, but I am assuming the drop in CL would also affect lift. Could be wrong, so don't run out and buy any lottery tickets based on my advice!
However if this is right then there will be insufficient lift produced by a wing to fly, and it is my own theory that the wind tunnel results are not real world. I can see that the force on the bottom of the wing needs to be greater (impact lift to give it a name), and in order for it to give more lift than the theory supposes, I can see that it is affected by the approach of the wing and is diverted downward before the wing actually passes, and so the wing is riding on a rising flow of air, so it planes, much as does a water ski. A well designed wing will be efficient because it reduces drag, as well as producing lift by increasing the downward flow of ambient air. As someone said, the total of all effects gives the lift; nothing is solely responsible.