Interesting. This suggests thinking about FAI not as using its control to produce terminal value in its own world, but as using its control to buy as much terminal value as it can, in various world-programs. Since it doesn't matter where the value is produced, most of the value doesn't have to be produced in the possible worlds with FAIs in them. Indeed, it sounds unlikely that specifically the FAI worlds will be optimal for FAI-value optimization. FAIs (and the worlds they control) act as instrumental leverage, a way of controlling the global mathematical universe into having more value for our preference.

Thus, more FAIs means stronger control over the mathematical universe, while more UFAIs mean that the mathematical universe is richer, and so the FAIs can get more value out of it with the same control. The metaphors of trade and comparative advantage start applying again, not on the naive level of cohabitation on the same world, but on the level of the global ontology. Mathematics grants you total control over your domain, so that your "atoms" can't be reused for something else by another stronger agent, and so you do benefit from most superintelligent "aliens".