I think the one thing the Scott Pilgrim film has going for it is that it's a rather organic companion piece to the books, from everything I've read. Started production right after the first volume was published and evolved along with the written series. Supposed to follow the first two books rather faithfully, then sort of goes off in its own direction, incorporating just the big ideas from books 3-5 and ending the whole thing in a unique way. I read there was also a lot of creative exchange between O' Malley the author and Wright, some of Wright's ideas and dialog finding its way into the later books and such even. And hell, the last volume hasn't even been released yet, set to come out some time this year, not even sure if it's before the film or not. I think this might be one case where it couldn't hurt either way to read the series before the film, since this is a particularly unusual case of adaptation. Not that I necessarily disagree with your logic for reading stuff after the film. Makes plenty of sense.