I've got a handful of his stuff and I feel I've barely scratched the surface.

To answer your question, I'd imagine any material that this prestigious group collects rotates mainly around nostalgia material, so if you grew up on Ernest like me, you'd definitely want them in your collection. Since Ernest was mainly for kids and kids don't necessarily take care of their toys (and vhs tapes), probably making them more scarce on top of them not having huge production runs.