There are a number of fonts here that are so similar to existing commercial fonts that it's can be extraordinarily difficult to tell them apart. I appreciate that fonts in certain categories are going to tend towards similar shapes, but the fonts I have in mind are handwritten fonts, which is where you'd expect the most individuality. This got me wondering about the way copyright law applies to typography... is it legal to recreate and publish a font that's all but identical to an existing commercial font?

No. It is not. Whether the existing font is commercial or not is irrelevant.