Our resources are finite. That is a simple fact of life, one which we must accept. The resources inside the Basin of Life are particularly limited. We cannot rely on the rest of the material plane to solve that problem. The Soulless gods saw to that. Fortunately, we are not restricted to the material plane. The resources of the other planes are also at our disposal. They are likewise finite, but they are vast. We need only reach out and take them.

Why bother? After all, it would take a great deal of effort to colonize the planes. We would need to develop specialized technologies to support new settlements and extract their resources. The colonists would have to abandon their other positions, which could leave our existing industries understaffed. Most of the planes are dangerous to those who are not attuned to them. Solving those problems would be a massive undertaking! What could possible justify it? 

The planes offer a chance at peace. Most conflicts are fundamentally economic in nature. The great powers compete over the few villages that have survived and prospered enough to pay tribute. Habitable space within the Basin of Life is limited, and so some cultures must fight over living space. An influx of resources could remove those conflicts. Of course, it would do nothing for the ethnic feuding of the Undervault or the theological spats between the unwise, but it would be an excellent start.

There is also the matter of security. The Basin of Life experiences a huge number of disasters, invasions, and other such unpleasantness. Granted, the other planes have their share of hardship, but problems in one rarely stretch to the others. The mortal races need not put all their eggs in a single basket. 

Of course, new resources are always welcome. Consider Emperor Ladantine's final example. He tapped into the power of the Astral plane. In doing so, he brought the Taint to the Basin of Life. Magnagora has since learned to harness that resource. It created entirely products and powers. Ladantine's execution leaves much to be desired, but it does show the potential power of the planes. We simply need to be more careful and refrain from putting stupid people in charge of large empires. There is even precedent for success. Aerochemantic techniques require resources from the elemental planes, but they allow for otherwise unprecedented feats. Other elemental planes, and even the ethereal plane, have spawned their own technologies. They are not as impressive, but they prove that nearly every plane has the potential to be useful.

Even basic resources have their uses. All environments have limited carrying capacities. They can only support so many people. Spreading the mortal races to new environments increases our maximum potential population. More people means more researchers, which means more technology. People beget progress, so long as they live in a reasonably sane society.

The general benefits of extraplanar colonization are clear enough. What of the individual planes? Where should people go? Where should we invest our limited time and resources? What can be gained from a given location?

The ethereal plane is a natural choice. It is fairly easy to access and offers an unusually hospitable environment. That makes it an ideal testing ground. The great powers of the world can use it to refine their transportation technologies and learn how to develop a new settlement. There is even a chance that the fae population can be put to good use. Their population is reasonably large, and they have a well-developed political system. Alliances are possible, and the subversion of their population is an option if they refuse. In time, they  might be tamed. The fae are relatively powerful as guardians of the wilderness. Imagine how much mightier they would be as the stewards of a tame, domestic garden!

The downside is that the ethereal plane appears to be best for producing fairly mundane resources. It has plenty of space, and it is highly fertile, so it is ideal for agricultural settlements. On the other hand, that simply gives us more of what we already have. Useful, but not vital. The plane certainly has unique power. The communes demonstrate that power well enough. The trouble is that their power relies on unreliable spirits. We cannot count on taming it, at least not for a long time. There is some hope for developing better techniques, as shown by the development of the Wildewood and Wyrdenwood technologies, but even they are primitive. It would be best to prioritize mundane settlement and growth first, so that the resources can help with later colonization efforts, rather than gambling on domesticated druidry.

The elemental planes are more promising. They are inhospitable, but they can support life. We need only find the technologies to settle them. That will be different for each plane, as will the benefits, but there are broad similarities. Colonists will need stable housing that can protect them from the elements, and they will need either the tools to sustain themselves directly or an efficient way to transport goods to the material plane without relying on specialized workers. A nexus of power can handle that, so long as the colony can supply porters for the goods, but there are security concerns with doing so. It would be better to have other methods.

The elemental planes offer a great deal in return for those efforts. They offer power. We can already harvest the essence of the elemental planes, but our methods are crude. We must hunt their beasts, and we are limited by their population. Domestication could save time and increase our supply. We might also learn to farm the local plants, on the planes that support them. Self-sustaining colonies are certainly possible, and they may be able to furnish us with mundane wares. Thus, elemental colonies have more to offer than ethereal ones, so long as we can overcome the local environments.

The cosmic planes are much the same, although they are also much more variable. The Continuum and the Vortex both have a great deal to offer, and their inhabitants are fairly tame. They are much like the elemental planes, in that they provide unique and irreplaceable resources. For example, Hallifaxian engineer has already proven the value of harmonics in a variety of fields. Flesh is less valuable, but sane engineers could likely put it to use. It has medical potential, if nothing else. Celestia and Nil are different because they have relatively intelligent inhabitants and fairly mundane environments. They must be viewed as hybrids between the elemental planes and the ethereal plane in every regard. They could likely support widespread habitation, particularly Celestia, so long as people adapted to their ecosystems and kept the natives under control. 

The astral plane offers the most interesting puzzle. It is clearly the most inhospitable. The odds of a truly self-sustaining colony are low, and thus any settlement would depend on support from another plane. The natives are inherently and utterly hostile to life. What could it possibly have to offer?

Hope. More than anything else, and more than any other plane, it offers hope for the future. Kethuru has taken so much from the world. Nations, races, places, devoured by the greatest monster ever to exist. We have lost innumerable treasures to Kethuru's appetite. 

In return, he spawns monsters to inhabit his prison. And yet, those monsters are a resource.  Their corpses can be offered to the Elder gods, and doing so appears to transfer their essence to those divinities. That reveals a simple, vital truth. We can rob Kethuru of its essence and put it to new uses. The scale appears to be negligible, so it unlikely that he can ever be truly destroyed or meaningfully weakened through that process, but we can recover what was lost. 

Perhaps we can only return it to the Elders in the hope that they will use it to make new things. Perhaps we can truly recover the lost wonders and restore them the world. Who can say? The potential is inconceivably enormous. After all, who could put a price on a mended world? 

That is precisely what an astral colony has to offer to us. It could serve as a research center, and, in time, a bastion from which we could march on the astral plane and recover the world's stolen essence. It would take a great deal of support from the other planes. It would take a massive effort. It would be risky, dangerous, and fallible. It would be worth it. For all that, it would be one of the greatest works of the mortal world, and a worthy use of our extraplanar resources.