N.B.: As this is perhaps the niche-iest books I've ever read, I am simply gonna write this as a chatty book report for my fic friend Jessi. The rest of y'all, feel free to stop reading; I won't be mad.
Hi sweet pea! Super jealous of your 3 a.m. lasagna.
Let me first of all tell you what may, for you, be the fatal flaw of Fangasm: it was completed in 2008, and took five years to find a publisher. Thus, it contains woefully little Misha; he shows up in the last chapter, is awesome and adorable, and then the book ends. This also means that the discussion of fic is limited to Wincest, which I know is on your NOPE list, and RPS, which is on mine.
But fic is actually a small part of the story here. It's a strange book, a hybrid of memoir and sociology (a little heavy on the former for my taste, but I'm kind of a jerk about memoirs generally). The authors, both college professors with real jobs and lives and children, document their trajectory as SPN fangirls. They discovered the show, then fic & wank, started attending cons (much to the chagrin of partners & children. I'm not gonna lie, were I a 15-year-old girl and my mom was flying across the country to ogle some hot twentysomething actor, I'd be mortified).
At some point, they had the admittedly brilliant idea to write a book about their fandom, which had the sneaky side effect of parlaying their academic credentials into access to the cast & creators. There are some great interviews in here: J2, obviously (and now I can say, yeah, they seem like nice dudes, but realllll ordinary. Whereas Misha? Total weirdo, hence one of My People), but there're also some nice moments with Jim Beaver, Samantha Ferris, etc. The more they approach BNF, however, they find the line between shrieky fangirl and serious scholar ever more difficult to navigate; eventually, their project comes to the attentions of TPTB and they're signed on to do an official book on SPN fandom (which comes with waaaaay increased access, natch)--but they finally realize that TPTB aren't interested in what they actually wanted to write about, i.e. fangirl guilt, shame, infighting, and above all, the sexual aspects of the fandom. (Because obvy, as much as they keep putting gorgeous people in our faces, TPTB don't want to hear about fan appreciation of such beauty, because Nice Girls don't have libidos.) Whereupon they were promptly dropped, slapped with a freakin' cease-and-desist order, and were left with a nearly completed orphan.
So. Would you like it? Probably, though it's not as insightful as Fic. I do like their notion that we all define "crazy fan" as the person juuuuuust over the horizon from where we're at, and they've got some smart things to say about how odd it is that a group of people linked by passion can clique off and turn on each other for not liking the same thing in the "right way." I really feel bad for Larsen & Zubernis having to wait so long to publish, because there's so much they weren't able to cover, and the book feels understandably dated. And also, it needs more Misha.