Another day of thinking about scenario 2 gave me a sci-fi idea: there's nothing stopping us here in 2-world from constructing "ships" that would reliably survive in 3-world. (Remember that 3-world is right here, around us, we just don't see it.) From our point of view the ship will self-destruct immediately upon launch, but the onboard computer will see a different picture: everything around it self-destructs and goes crazy, but the computer itself becomes awesomely powerful and can solve NP-complete problems in polynomial time. The idea is essentially identical to quantum suicide computing or reality editing. Of course, such a machine can never go back to our world.