If you have access to a parts tumbler, they can be very beneficial to the DIY'r especially with mechanical restorations. The small one from Harbor Freight for example, will suit most needs. Depending on the media used, they are wonderful for restoring the finish, removing corrosion and finishing metal stampings with production parts, hardware, tools, bolts etc. Go on Youtube to see the results. The plate is a great candidate for this.
You can sometimes find them used in the classified postings and they are not hard to build.