> What's the appeal of this compared to a cheaper and more powerful N150 NUC, or a used mini PC

This is a very good question. The Pi 500+ is a beautiful product, but when compared in terms of price/value to the NUC and various other mini PCs, its value proposition is questionable.

Perhaps the target group are enthusiasts who had 8/16-bit "all-in-one" computers like Commodore64, Amiga, Atari, ZX Spectrum, Acorn etc., in their younger years and now want to buy something similar (non-x86) for themselves or force it on their kids. :)