Giving Mars an atmosphere is pretty much out of the question. Even digging a 20km deep hole in Hellas Planitia to achieve a pressure above the Armstrong limit is more plausible.
The problem with interstellar travel is that the distances are so huge that there is a high probability of having a catastrophic crash. Particularly at the speeds required.
VR is going to help in this regard. Will VR be able to be a good replacement for a walk over the forest? I think it will. I didn't need VR to trade my outside activities for indoor, climatized comfy online ones. Although it's probably true that spending years inside a submarine isn't for everyone.
Replacement doesn't necessarily means it will be identical. It could be an inherently different but superior experience. Of course it would only work for people who isn't in denial. ^_^
