Our club is very lucky. The landowner let us put a sea-container on the property for storage and we leave the pads out in the field the whole 6-7 months of the season.
Because of that, the club only cleans our rails once a year with Scotch-Brite pads and WD-40 before the season, during our maintenance day. The rails get put into the sea-container at the end of the season, but the pads sit outside during the off season. We finally replaced the rails after 11 years because the anodizing was starting to get bad in places from exhaust and years of Scotch-Brite pads. The 1010 & 1515 pieces the pads are made out of are dirty, but still in good shape after 12 years. I don't think they have ever been cleaned other than the rain washing them, off so their anodizing is still very good.
There are a few folks that will clean a rail once in a while during the season. Usually with the Scotch-Brite pads and WD-40. We haven't found that dirty rails have any detrimental affect on flights or the rails themselves since only the edges of the slot contact the rail buttons and the slots stay pretty clean with use. They may not look so good, but they work just as well dirty at the end of the season as they did clean at the start.