I don't see much difference in conductivity between tin coating and steel rails - you have to get a good electrical contact between the rollers and the rail. Sparking or poor engine operation would indicate a cleaning is needed. The tin plate is corrosion protection and I have not noted old and tarnished track having a problem - the key to good conductivity is a clean, corrosion-free, surface for roller and wheel contact.
Since my "layout" is a collection of modules stored in a not so "cool dry place" between club shows, I get grunge and corrosion on exposed tubular rails. Rather than replace track, I have been using metal polish to clean the track to a shiny surface on the rail heads. The brand of metal polish doesn't seem to matter and Brasso works as well as the more costly brands. Some of the track lost it's tin plating years ago (probably from aggressive cleaning with Scotchbrite pads) and the polish removes light rust in addition to oil and dirt. Using soft cloths instead of Scotchbrite is probably a bit kinder to the thin tinplate coating on modern track.
I also note that ever since smoke fluid (a light mineral oil) became a staple for running trains, the oil film on the rails after a show prevents rusting for a while. Modules cleaned with alcohol or other solvent before storage begin rusting much sooner. (There was a thread some years ago advocating wiping track with Wahl clipper oil to prevent corrosion.) Accordingly, my modules get put away wet and cleaned immediately before the next show.