To refinish my floor plates I degrease them using gun scrubber or some other lung searing industrial strength cleaner, then I dip them in Birchwood Casey "ALUMA BLACK". (Let them sit for 10-30 seconds which should cause some bubbling at the site of the scratch) Then rinse with cold water.
This works and works real good. However, if it's just scratched, you'll still be able to somewhat notice where the old scratch was. Apply a light coat of CLP which should help to hide the scratch even more.
If your floor plates are really toast or if you don't want a trace of the scratches, and if you can get to a sand-blaster, hit them GENTLY with small grit sand. (Although I have used copper slag which was really large and they turned out OK) Then submerge the plate into a container of the ALUMA-BLACK. ***Note, as the solution bubbles on the aluminum there is a bit of heat given off as well as some NASTY vapors. I advise doing so in a well ventilated area to avoid seeing zombies! Once you've rinsed them in cold water apply CLP for a nice sheen. They should look good as new.
The nice thing about this method is that, unlike painting them, the finish won't chip and is not easily scratched off.
Sly