I think a great way that humanity could repay the planet for all the damage we're doing is if we could prevent the next large-magnitude extinction event. Of course, in order to do that, we need to figure out how to sustain human & other life on our planet until then. The next thing we should do is set our eyes on spreading Earth-bound life to other bodies devoid of their own life, but until we can learn to live together and within finite resources, any such project (at scale) is doomed.
I once heard a claim that resonated with me, and I'm pretty sure it's true: the least hospitable place on the surface of the Earth is more habitable than the next-most hospitable place in the solar system. Terraforming Mars looks completely infeasible for multiple, fundamental reasons. Even if we can make colonies on the moon and Mars self-sustaining, how long do you think they'll last? Maybe 10k years? That's a drop in the bucket, compared to even hominid life on Earth. There's really no getting around the fact that we need to figure how to make the life-sustaining capacity of the Earth last.
Hoping someone, someday finds an archive of our information is a nice idea, and better than nothing, but it's pretty small consolation. Also, I'll bet the project considered this, but I'd be worried about the nano-film getting degraded by cosmic rays and such. And then there's the risk of it getting buried by dust - maybe kicked up by meteor impacts, but Mars also has enough atmosphere to blow around the stuff.