I may be repeating myself, hope not, but I have two comments. An excellent and experienced modeler whom I admire for his expertise and skill is Doc Wayne over on the MR forums and who runs his own in co-operation with some friends, called Big Blue (The Gauge), has spoken about his experience using lacquer thinner to clean his rails. That compound, a real compound and not something like paint thinner or varsol, has toluene, xylene, and other nasty things that, combined, do a superb job in Lifting organic matter from rails. It leaves almost no discernible residue that he feels makes it less than very darned good for the use to which he puts it. I have yet to try it, but I suspect I will.
Secondly, on a whim I decided to liberally coat the rails on my second layout, a couple of weeks before I was to tear it down (thinking I had nothing to lose...) with Dextron III Mercon auto-transmission fluid. I had been convinced long since to lube my steamers' outer works and axles with it, which has worked very well with no mechanical failures or marred paint. Dextron III Mercon is plastics and paint safe BTW, and was recommended specifically by a chemical engineer on MR forums. Also, it won't affect traction tires by destroying them over time. Anyhoo, I coated my rails on my main loop and began to run trains. My main had 3.5% grades, fairly stiff even by model train standards. I could detect no slipping and no stalling due to apparent electrical issues. This was the case for the next couple of weeks.
Actually, one other point. I have used 600 grit paper, alcohol, WD-40, and other things trying to make my track nice 'n shiny and for it to stay that way. No matter how often I do these things, on any second day I can wipe the rails with a clean dry white bed sheet remnant and have it come away with grey streaks. The only people who broadly claim that it doesn't do that for them are those who purport to have undertaken the process called 'gleaming'.
Why is that last point important? Because I don't think it's a problem, and I don't think it is anything more than a bit of oxides from burnt dust settling every second on your rails and carbon from arcing between the metal tires that have pickup wipers on them and the energized rails. You could wipe your rails until the cows come hope, turning the cloth to a new side every time, and it will still come up with the grey streaks.
Okay, my final point: I think the guys who have settled on quality metal tires and who run their trains fairly often are onto something. They almost universally claim that their dirty track, or electrical problems, go away when most rails and all joiners are soldered and fed, and when they run trains with almost all metal tires several times each week. Something to think about.