i am running largescale trackpower trains on brass for over 50 years now. (mostly LGB and Playmobil)
apart from the locos and 1 (in words ONE) two axle postcar - everything runs on plastic wheels. (edit: not true. i have one car with crude ironwheels from our village smith)
yes, there is some build-up of of dark dirt on the rails. so what?
only when i had my layout outdoors, i had to clean the track more than once a year.
as most of my locos have power pickup skids they grind the rails enough, for power pickup.
(LGB and Playmobil plastic wheels seem to be made of more resistant, tougher plastic, than the other brands.)
yes, roling stock with metal wheels have more weight, and as low as possible.
but steel wheels also are a big weight for ones purse.
so in my first decades of cheapscate largescaling i used buckshot, fishingweights and carwheel weights. (for the price of one set of steelwheels i could weight down a whole train.)
and now? - now i'm too parsimonious* to change the wheels of 40-plus cars. (cigarettes, booze, computergames ... so many other essential things i can spend my money on...)
*( had to look up this word, because i suppose, that the word for closed pockets, that i learned decades ago, would stirr up the wokies, because it starts with "n" )