Nikon SB-900 Speedlight?

If I use the SB-900 on TTL to take pictures of a wedding or birthday party will I notice anything better in the images compared to taken with a SB-600 on the same or almost the same settings?

The SB-900 is a much more advanced flash unit and has a little more powerful output.

Guide numbers:

SB-900 = 34 m/111.5 ft.
SB-600 = 30 m/98 ft.

Probably not (unless you need the extra reach of the 900).