>they scale well with number of members up to a point of four or so, where adding another participant generates more ideas than it costs time.

That's the main thing I come across. Most meetings are well over four people. And personally, I already don't deal well with more than 3 people as most people work on a vastly different wavelength than myself.

Now consider all the "Agile" meetings are already 5+ people and often contain management types and people who are both higher on the chain of command and have no technical background either hogging the attention. Suddenly, most meetings I see become either a hybrid announcement + roll call, a "meeting" with ulterior motives (e.g. managers trying to measure "participation" as a way to grade employees) or a very rushed design-by-committee approach to solving something.