The Buss plugin does model the summing bus part of the desk, so it's part of the overall sonic package. Each VCA group, controlled from the Buss plugin, controls the Channel plugins assigned to that group. The VCA groups do not add any coloration on their own; they just provide an easy way to change the Channel settings within a group.
The main point is that the large controls along the top of the Buss plugin affect the overall sound of the mix, while the smaller VCA controls affect the sound of the individual tracks assigned to that VCA, as if you were changing the settings of each Channel plugin in the group.
There are no specific rules on the use of the Drive or Noise controls, so it's always good to set them according to your track's levels and the amount of coloration you want. Although, I'd say it's best not to overload the plugins -- they sound better to me when the meters aren't moving too much, say up to -8dB or so.
The simplest way to use NLS is to insert a Channel plugin on each individual track (using a different console channel preset for each) and one Buss plugin on the Master track, leaving all Channels assigned to the default "Grp1" group. Then you have just one VCA Group to worry about. I usually put NLS as the first insert and use the output faders to help with gain staging.
Once you get used to using it that way, you can experiment further by assigning all Drum tracks to a Drum VCA, Keys to their own VCA, etc. Then you can go nuts trying various Desks and Drive levels within each group. :-) You don't have to add more Buss plugins for each group, since you can control all of them (up to 8) from the main Master Buss plugin.
As an aside, I was demoing the new UAD SSL channel strip recently and comparing it to the Waves equivalent. While the UAD clearly sounded better to me than Waves by itself, adding NLS to each channel (on the "Spike" setting, naturally) closed the gap considerably. I'd say Waves SSL + NLS is a great combo -- I still think UAD wins, but not by much. I preferred the Waves combo over the new Brainworx SSL console as well. YMMV.
Hope this helps!
Cheers,
Eddie