Great niche tutorial here. Thrift stores by me always get a big head about these and overprice them. Perhaps the market has dipped since the 90's because that generation has passed on and the same passion wasn't handed down.
Sadly, I find a lot of the plates, but most have almost no resale value. I almost always ignore the figures these days due to repairs or pricing (but now I have a little more intel on how to ID them). Perhaps this is a sign to keep a closer eye out soon.