I've never had a conductivity issue with fastrack. Passenger cars seldom even flicker over the switches.
I occassionally ( 2 or 3 times a year at most) wipe it down with 91% isopropyl when it looks dirty or when sound on a Legacy loco cuts out.
If I have any stubborn buildup. I run Lionels abrasive eraser over the track, then wipe it down with the alcohol.
IMO,Rail zip or not, theres simply no substitute for cleaning the track.