squirls β I don't know of any specialist plinth collections, but I am sure that there must be some! I would find a reference collection useful for a variety of reasons.
There are both great rarities and eclectic exotica in the world of plinths. Davidson orange cloud and ORA (red cloud) plinths are rare.
The best known peculiar shape is the clover leaf shaped Sowerby plinth made to fit their 2525 "frog" bowls and vases. Another fine plinth made by Sowerby is the waisted plinth made to fit the large 8" 2614 "elephant" bowl.
Jobling plinths are all very similar, but there are two variants worth looking out for. One, I think, is for the crinoline lady centrepiece set and is reversed, i.e. the bowl fits over a central raised area, and the other has a very wide rim to fit the medium sized bowl of the dancing lady set. Bagley produced some fine oval and diamond shaped plinths.
The aristocrats of plinths come from central Europe, apparently mostly from the old Czechoslovakia. Many of these are magnificent creations, and can be quite scarce.
A cautionary note. The value of a centrepiece or other set lies in the complete original set as issued by the glassworks and sold by the retailer. The components on their own are just spare parts with a corresponding value, although somewhat more than ".25", whatever currency you use. Please keep complete sets together, unless you are extremely wealthy and have money to burn, in which case please send your surplus cash (all currencies accepted) to Bernard Cavalot ...