Nitrogen filling won't affect ride quality but maintains pressure in the tyres for longer duration than normal air. I am also running with nitrogen in my Swift (Nitro, eh!
) but didn't feel any difference in ride quality.
Yes I agree that the car moves like a Bolero! Either left either right! I think this is because of self centering action of steering. I noticed this on a long curvy road on my trip to Uttarakhand and if you leave the steering (I mean don't hold it firm) it starts pushing back to original position which means the car deviates from line. This thing is
TOTALLY absent in my 2009 Swift where self centering action isn't prominent as Baleno. RM said that it will be checked at first service as steering usually becomes smoother after use and it is not expected that problem will go away on its own. Let's see.
Yes I also felt that rear wheel arch cladding is different from front cladding. There is a felt covering on the outside, though I didn't check if it is cardboard or plastic on the inside. I think the material is same on all wheel arches and rear one is covered additionally to reduce road noise.
Also, you are right about cruising capability of the car. At 80 kmph, engine feels at home and maintains the speed easily without any effort.