Interesting, I have the opposite experience. I much prefer walking in streets designed by central planners to accommodate modern crowds (Singapore, central Beijing, central Chengdu...) than twisty narrow streets there for historical reasons (Hong Kong, especially the stretch from Central to Sheung Wan, especially on weekends; but also the "preserved" hutongs in Beijing).
The reason is crowds: try walking through Sheung Wan, or Singapore's preserved shophouse streets in Chinatown, on a Sunday afternoon and see what average speed you achieve... And you can also spot crazy drivers better in a large, wide-roaded grid than round the corner of a hutong where you have to spot the direction of the rapidly approaching noise so you know which side to jump. Not to mention: the sun can actually shine if the roads are wide, in tight streets you are in the dark even at lunchtime.
Smog is a problem which can be solved, as much of Europe and the US have demonstrated. China will eventually move industry out of the cities and drive with catalytic converters.
Where tight streets might win is when they are coupled with a pedestrian area. "No cars" is still the most pleasant walking experience.