Re: brass track.
The brass track is just as good a conductor as nickle silver. The problem comes with oxidation - the oxides of nickle silver conduct electricity, while the oxide of brass does not. That means that your track should be very clean, regardless of whether it is NS, brass or something else.
If you have brass track, I would say use it for now, unless you want to spend the money to replace it. You might try a very, very small amount of clipper oil once you have cleaned the track. This will help improve conductivity, and slow the oxidation. See Ralph's "Great Wahl Clipper Oil Experiment" thread in the General Talk forum.
Andrew