Fantastic Find!!!
A Confederate belt plate in near perfect condition is indeed a rare find. As described by TheCannonballGuy, this particular waist belt plate was originally intended to be a utilitarian as well as decorative fastening for a more simple belt worn by standard infantrymen in the Confederate service. The Model 1851 Federal Sword Belt Plate you found earlier, would have in fact been utilized by cavalrymen on a belt for carrying sabers, as well as for officers of various rank and branch, in carrying swords.
In regards to cleaning, my sentiments entirely concur as well. The find looks great as is, and anything more would surely be detrimental.
CC Hunter
P.S. If you are not already aware of the fact, one of your eagle buttons found during an earlier hunt, is a Confederate Staff Officers button! These are also quite desirable and rarely found buttons.