Hi Michael, welcome to the forum.
Generally, if the track is already laid, the only effective way to take off the shine is to use a fine brush. Adding a little grime and rust here and there. If you can do it before you lay the track you could airbrush it.
For ballast, an airbrush is the easiest. Depending if you run steam, electric or diesel, the ballast with be dirtied in different ways. Research what you are looking for by studying photos of the real thing. Mask the tracks and apply the grime. Apply light coats and build it up. Keeping the mask off the track will obviously dirty the track too, but sometimes the ballast may have black grime, but you may want to keep the rails red with rust. If that's what you're after, you'll need to mask the rails.
I lay ballast and then use my airbrush to take the 'newness' off a bit. I use a dirty grey/brown.
Remember that stations, sidings and loco yards will have more grime. This is where the crews would oils and clean the engines so ash and oil would be everywhere. So a loco yard would be a mucky place.