Are your staging tracks a visible part of the layout? Often times if the tracks just run off the layout onto a shelf, "off stage" from your layout where the show is put on, people tend to simply skip the scenery on them. Most modeler's realize these tracks are the "backstage" of our layouts were we store trains and serve as fiddle tracks or where the 0-5-0 does it's work. If your staging tracks are on a highly visible section of the layout, then yes you may want to disguise them as a yard.
The spilled coal depends on what, where and when you are modeling. Mines used to separate the coal by size. So the first track under the coal tipple could be fine crushed coal, the 2nd medium crushed coal, the 3rd track loading large chunks, etc. Over time mines discontinued doing this and simply produced one size of coal. I don't know exact dates, and again even that can vary per mine, but from my research the shifting away from sizing coal began prior to WWII and on through the transition era.
As for how much coal they would have spilled; Coal was their revenue product. Spilled coal is lost money. The tracks won't be clean, but there would not be an excessive amount. If there were piles of spilled coal large enough for someone to be able to shovel up, then they would have. Coal was money.