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. ^_^
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.