“Please don’t read this as repudiation of Agile methods and advocation of “big requirements up front”. ”

Sorry, but Mr. Ambler and others will read it exactly this way. What is needed to take out the word “big” from that tortuous phrase and replace it with “enough” or “sufficient”. Other than that, practitioners will either do what you describe, or not, with sufficient justification needed to convince project sponsors that what they are doing is right….until it isn’t.

The thing is, either approach can work; I just get tired of anyone who says only their approach works, whatever it is.