given that minimising uncertainty is one of the tasks of management, how much effort should managers put into?

Answer 1

One can prepare all efforts into minimizing uncertanity, but what is a sign of good management is the ability to adapt to uncertain situations and to be able to adjust in a professional manner to all types of circumstances.

There should be a "plan" to adjust according to "out of the ordinary" practices. Business needs to take precautions and be comfortable in its ability to adjust accordingly. Whatever amount of time that is necessary to accomplish that goal is worth the efforts.