My rule of thumb is: if it is not in the Silmarillion I tend to ignore it. I first read it in ‘86 and didn’t read HoMe until I had already begun writing fanfic. And it never caused me to alter my headcanon that had been brewing for decades. Not that there’s not some interesting things (Morgoth’s Riing is my favourite) but nothing that I can’t do without. And overly scholarly works turn me completely off. I like there to be a decent internal logic and knowledge of the history of Middle-earth of course, but if people begin using fic to showcase their scholastic attainments in the field, it shows, and just makes me snore. It’s not storytelling, to me, it’s more like an essay.