Not sure if this is "known" around here yet but my father showed me this when we use to work on cars.
We use to use 3m marine restorer and polish on metal parts that were faded and had small spots of rust. Here is what it can do...
My dome light had some small that spots and heavy build up on it, possibly from cigarette smoke and years of sitting, I hit it with the polish and then some turtle wax to protect it.
It's not the cure all, end all and doesn't always work but when it does it can save you some money and is like magic!