Which stage of effectiveness matters most?

Many altruistic endeavors seem overwhelmingly likely to be ineffective compared to what is possible. For instance building schools, funding expensive AIDS treatment, and raising awareness about breast cancer and low status.

For many other endeavors, it is possible to tell a story under which they are massively important, and hard to conclusively show that we don’t live in that story. Yet it is also hard to make a very strong case that they are better than a huge number of other activities. For instance, changing policy discourse in China, averting rainforest deforestation or pushing for US immigration reform.

There are also (at least in theory) endeavors that can be reasonably expected to be much better than anything else available. Given current disagreement over what fits in this category, it seems to either be empty at the moment, or highly dependent on values.

An important question for those interested in effective altruism is whether most of the gains from effectiveness are to come from people who support the obviously ineffective endeavors moving to plausibly effective ones, or from people who support the plausibly effective endeavors moving to the very probably effective ones.

One reason this matters is that the first jump requires hardly any new research about actual endeavors, while the second seems to require a lot of it. Another is that the first plan involves engaging quite a different demographic to the second, and probably in a different way. Finally, the second plan requires intellectual standards that can actually filter out the plausible endeavors from the very good ones. Such standards seem hard to develop and maintain. Upholding norms that filter terrible interventions from plausible ones is plenty of work, and probably easier.

My own intuition has been that most of the value will come from the second possibility. However I suspect others have the opposite feeling, or at least aim to exploit the first possibility more at the moment. What do you think? Is the distinction even just?