Just popped in my Sin City DVD for the first time in ages.  I still have a big issue with the CGI in the movie, you know that they're not really in the locations... especially when they're on the treadmills.  And everything in that world is sort of soft and cartoonish... none of the places really feel REAL, you know?  I really hope that in the time span between the last flick, RR had the sequel in the back of his head and so was just taking reference and plate shots every chance he got.  I know I would have been.  Maybe even go more noir style, shoot back projection style shots for when they're driving.

And I'm also really hoping that they bring people in... I like that RR does so much himself, but his films are missing something because of that.  Anyone would be eager to work on the next Sin City so you know he could bring in some brilliant talent for some stuff like Fincher-style opening titles.

And since current digital cameras get you sharper pictures and pick up more light, you could get a little more experimental and extreme in the shots.  Get more of that stylized lighting in camera on the day rather than play around with it later, you could tell when they did that.
That and the elements, remember the rain at the start making those fakey puddles?  That's gotta change.

As much as we liked the first one, it should be a proof-of-concept for what the second one should be.