I would definitely opt for night/day changes and also weather as well.
Pedestrians wouldn't need to be GTA style, there are games where it is impossible to run pedestrians over because they just move out of the way, I think it would make the whole experience just more realistic.
Much improved trading system is needed where you can choose who you can sell a car too rather than just putting in the bigger trade pool.
I agree with removing the shops and maybe just having smaller clothing options so not every player is a clone of each other, unless there is more interation with the character but then that changes the style of game really.
Damage is interesting, if it is an option it means people will be playing different types of game so if some earns a million with damage on are they a better player than someone earning a million with damage off? If you see what I mean.
I kind of like the idea of different kinds of vehicle, remembering this is supposed to be the ultimate lifestyle experience so perhaps not bangers but luxury 4x4s like Range Rovers and so on would be good I reckon.
GC