Is the idea of prayer circles and/or mass meditations a good one for specific purposes like rescue missions for off-planet slave colonies or other rescues like North Korea?

This is a quite beautiful idea and fits in with the process you already use in your Lightworker Healing Protocol for the group collaboration; to have a healing circle of like-minded individuals contributing to the betterment of a target client group which, as you know, can be done on any scale. The informal meditation groups come together, often with only the vaguest idea of what the benefits might be, and often the desires and intentions are quite lofty, but also quite broad and lack focus and definition of particulars. And this does limit their reach, because the energy will dissipate, accordingly. It is sort of like spreading seeds for planting. If you scatter them between the feed store and the farm, many will fall on fallow ground and will not bring forth useful plants, whereas those planted in a pre-plowed row will be nurtured and watered by human love and consciousness and divine watch, and are in the starting place that is ideal for them to flourish, to grow, find roots and create plants that stand tall in the sun and bring forth a bountiful harvest.