Hi Stephen,
I see from the EXIF the first shot was 30 seconds at f/22.
As an exercise, you might want to try shooting it throughout your aperture range for the same expsoure to see what that does result in for star points, etc.
e.g. f/16 at 15 seconds, f/11 at 7.5 seconds and so on.
By the time you get to wide open (f/3.5 at 18mm?), the stars (on lights) will have gone (hopefully the others will remain).
I'm afraid I have little experience night shooting myself, having only tried recently with a P&S for some city scenes (handheld
)
Good luck,