Protectoplates were metal plates embossed with the original owners name and car ID data on GM cars. They were issued to the original owner of the car and came attached to the back cover of the warranty book.
They're nice to have & add to the originality & documentation of a GM car but very few survive the changes in ownership over the years.
I would probably buy a reproduction if it were high quality and looked like the original just to add it to my collection of stuff on my car. I wouldn't consider a repro protectoplate in the same negative light as reproducing a VIN plate or cowl data plate as it cannot be used to make the car something it's not (i.e. turning a clone into a "real" GTO). Unfortunately, there are some unscrupulous folks out there who will have one of these made and claim it's the "original" protectoplate for their car just to justify a higher asking price.
Just my 2 cents.
http://kurtspontiac.homestead.com/TimSimpson66GTO.html