A semiconductor die assembly in accordance with an embodiment of the present technology includes a first semiconductor die, a package substrate underlying the first semiconductor die, an interposer between the package substrate and the first semiconductor die, and a second semiconductor die between the package substrate and the interposer. The semiconductor die assembly further comprises a heat spreader including a cap thermally coupled to the first semiconductor die at a first elevation, and a pillar thermally coupled to the second semiconductor die at a second elevation different than the first elevation. The heat spreader is configured to transfer heat away from the first and second semiconductor dies via the cap and the pillar, respectively. The interposer extends around at least 75% of a perimeter of the pillar in a plane between the first and second elevations.