[Gregaros]

>Shouldn't imagination and planning be observed spontaneously as emergent properties of a sufficiently complex neural network?

Why would you think that? We have no theoretical knowledge of how human "consciousness" emerges, and obviously no experimental data either.

>Conversely, if we have to explicitly account for these properties and come up with specific designs to emulate them, how do we know that we are on the right track to beyond human levels of cognition, and not just building "one-trick networks"?

We don't know how far the path leads, but the capabilities of the past 5-ish years progress are leaps and bounds beyond what anything else can do, and this is part of the work of pushing further down that path.