What if we moved a large asteroid to a highly elliptical orbit between Earth and Mars and then occupied it like we occupy the ISS?
It'd be a slow trip to Mars, but if we're in no rush, we'd get free transit between Earth and Mars. Sort of like a super slow postal service.
Would make a good bridge between the two nation planets once we populates the red one. Would also give free resources, maybe water and some raw materials to build with.
Possibly some good shielding from harmful solar radiation, too, if you're cool with building your asteroid abode several feet underground to block out the energetic rays.
You could keep the asteroid and Mars both permanently occupied, and if something went super wrong here or there, there would be a chance that the asteroid would be coming around in a month or two, just in time to launch from their fly ships toward here or there and document what went wrong.
They wouldn't do much to help, but they'd maybe take over once it was safe to do so and help rebuild, I guess.
To clarify, my dumb idea is not to use an asteroid like a spaceship (launching from planet to planet with huge delta V costs)... but rather to put it in a very stable orbit so that it's there for thousands and thousands and thousands and thousands of years.
...The upfront cost would be earth-shattering, yes, but the results would be fairly permanent and whatever benefit we might get out of them, we'd enjoy... practically forever?