Todays equivalent would be those Funko PopVinyl figures. I'm amazed at how many people thìnk they are worth something when theres hundreds of rudimentary looking figures for every cult favorite movie, videogame, and cartoon.
The hype around rapidly increasing values on Pop Vinyls has largely gone, the market seems to have chilled and the reason it hasn't crashed likely to be because of the value attached to the licenses.
The most interesting part of the whole thing I found was the effect valuing sites had on the market (i.e. poppriceguide). They significantly lowered the effort in determining value for existing collectors and attracted a lot of people whole wouldn't normally collect to get into it purely for the profit to be gained. I am not suggesting others wouldn't have been attracted to the market without them but having the data readily available rather than having to trawl eBay completed sales lowered the barrier of entry.