They won't make microgravity suffer, because even if they weight the ship down, they generate lift which more than compensates for extra weight.
That way, they would improve the survivablity of the pilots, by providing pylons for armament, extra lift and booms for manouvering thrusters.
As for atmo missions and R2, I'm just a texturer, so I don't know what the team is planning, hence why I said that an atmo mission "should" be in R2.
Also, I did not said that it'll be in campaign, it could be a single mission just as well (and propably will be, the mars city assets are just too awesome not to use).