While it's important to clean the track many modellers will suggest it's at least as important to ensure that all wheels are clean including and especially those that are fitted to rolling stock, tenders or any other unpowered wheels on locos. When I first started modelling in S4 it became very noticeable that the build up of crud and gunge was enough to cause derailments and when I'd gone through and cleaned all my wheels thoroughly not only did the derailments disappeared track cleaning became much less of an issue. I had a layout at the last 4 day York Exhibition and only cleaned the track during setup. Never needed to touch it all weekend and also noticed that any derailments were generally operator error.