Calling all armchair generals! Boudica's Last Stand.

[Renatus]

I cannot resist mentioning that all this planning, conspiring, mass deception and careful preparation would seem to be the direct opposite of incuriosus, 'careless' or 'negligent'...

But I am increasingly thinking that we cannot really take Tacitus on his word about all this, so we are back to square one...

There's no need to throw the baby out with the bathwater.  Lewis & Short (and my even older dictionary) defines 'incuriosus' as 'careless, unconcerned, regardless, indifferent'.  In this context, it only means that they did not bother to sow crops.  It has no bearing on any other preparations that would have had to be made.