Giving diminished returns on some valuable quantity X, equal distribution of X is preferable anyway.

I think you're quite confused about the constraints imposed by von Neumann-Morgenstern theorem.

In particular, it doesn't in any way imply that if you slice a large region of space into smaller regions of space, the utility of the large region of space has to be equal to the sum of utilities of smaller regions of space considered independently by what ever function gives you the utility within a region of space. Space being the whole universe, smaller regions of space being, say, spheres fitted around people's brains. You get the idea.