Nice Thread Nick! And nice avatar, never saw that one before-great photo.
Each of these boats has an interesting story, and as the next caretaker you'll add your own.
I would urge you to replace the plate upon finishing the vessel just as I would urge you to eventually replace an aluminum mast with a wood one if your boat had one.
Yes, you are probably right about the occasional plate being stolen, more frequent and problematic for provenance over the years have been owners that kept the plate as a keepsake instead of letting it go with the boat.
Thieves have stolen entire boats, and wrecked them in the S-Class. We've had a devil of a time reconciling which boat was which and what it's final destination because in part owners took the plates off some of boats, name changes, borrowed sails, etc. which one was wrecked, which one was demolished/parted out. I think you get the idea.
The value of boats without their plates especially in the one-designs is somewhat less as well.
You want to be a good steward. I would urge you to replace the plate and polish from time to time. You've made a great start, and I think most everyone that follows the registry is quite happy you've rolled the dice with Lady Luck.