Well, this is morality we're talking about, right? So in that case we should ask ourselves what we want.

Let's say that there are already 10^10^20 people out there, and you're suddenly blessed with a thousand times the resources. Would you rather have 10^(10^20 + 3) people in existence, or raise the standard of living by a factor of a thousand?

To look at it another way, let's say that you recently glanced up out of the corner of your eye and saw a dust speck. I have a thousand units of resource. Would you prefer that I simulate a thousand different versions of Robin who saw the dust speck in slightly different locations in a 10 x 10 x 10 grid, or would you rather have a thousand times as much money?

For me, the value of creating new existences is linked to their diversity; as you create more people, you run out of diversity, and so it becomes more important to create the best people rather than to create new people.

Suppose that Earth were the only planet, the only branch, and the only region in all of existence. Then we might want to have mathematicians share all possible developments with each other, in order to prevent them from duplicating each other's work and let them prove as many new theorems as possible; because if someone here doesn't prove a theorem, no one will ever know that theorem ever.

But if there are zillions of Earths, then mathematicians may want not to peek at spoilers, saving the joy of discovering especially fun theorems for themselves - they will concentrate on individually experiencing the highest-quality theorems, rather than trying to cover as much space as possible as a group.