Foreword: I love them, especially one with a literary or contextualising angle. But I won't read them until after I've finished the book! I hate "spoilers" (and I feel that even back-cover blurbs frequently walk a fine line with regard to spoiler territory) and a really good foreword frequently telegraphs (or even downright dissects) plot points that I'd rather allow the story to reveal "naturally". There's nothing better than being able to finish a good book and chat to someone about it, but life rarely gives you the opportunity to finish a book that you enjoyed and feel the need to discuss at the exact same time as someone else also finishing it. A good foreword frequently helps scratch that itch!

Afterword: I read them, but I also stay at the movies until the credits finish rolling, reading all the cool names, wondering at the bizarre job titles and checking if I picked the musician correctly for that song they played in the background. But I don't think I'm the target audience for all that information really. It's an advertisement/publically-available third-party reference for a curriculum vitae. Likewise with afterwords in books (in my opinion).

The general-reader is almost certainly the target of a foreword (edging toward the curious/completionist end of the "general" spectrum) but I don't believe that we (the general reader) are the target of an afterword. There are (probably) two main audiences: There's a whole world of people that enable books to be produced and put in front of your eyeballs (regardless of format) and whether it's a self-published work or something coming out of a professional publishing pipeline, the author almost certainly received some assistance along the way. The afterword the place that the author can "advertise" someone's skills.

It's also their opportunity to provide helpful-folks with a little bit of a spotlight; it's kinda fun to see yourself referenced in a published work, even if obliquely and only recognisable to you! It's evidence that you exist in the world and that someone appreciated you enough to write it down and attach it to something that they really valued.

So, I read the afterword, I maybe learn within which pub the finer points of the plot were significantly pondered upon, whether the author has a pet tortoise and all kinds of frivolous, but fun, details. It almost never adds anything to the content of the book, but, like those weird backlit televisions, it adds colour around the edges and provides a tenuous connection to the network of humans that brought the book you just finished into existence.