This is fun!
Why reward for sticking to the pact rather than punish for not sticking to it?
How is it possible to have any causal influence on an objectively simulated physics? You wouldn’t be rewarding the sub-universe, you’d be simulating a different, happier sub-universe. (This argument applies to simulation arguments of all kinds.)
I think a higher-complexity simulating universe can always out-compete the simulated universe in coverage of the space of possible life-supporting physical laws. You could argue that simulating lower-complexity universes than what you’re capable of is not worth rewarding, since it cannot possibly make your universe more likely. If we want to look for a just-so criteria for a pact, why not limit yourself to only simulating universes of equal complexity to your own? Perhaps there is some principle whereby the computationally difficult phenomena in our universe are easy in another, and vice-versa, and thus the goal is to find our partner-universe, or ring-universes (a la https://github.com/mame/quine-relay )?
Another neat direction this work can go in is toward corroborating the computational feasibility of simulationism and artificial life.
If abstractions are natural then certain optimizations in physical simulation software are potentially not impossible. These optimizations would be of the type that save compute resources by computing only at those abstraction levels the inhabitants of the simulation can directly observe/measure.
If abstractions aren’t natural, then the simulation software can’t generically know what it can get away with lossily compressing wrt a given observer. Or something to that effect.