I'm somewhere in the middle. I wouldn't have bought and played Undertale if I hadn't had one of its twists spoiled for me (because that's when I knew I would like this game), but I would probably be planning murders right now if someone had spoiled the major twists of my favorite visual novels. When it's not a big thing or something you're supposed to realize on your own over time I can usually enjoy the story just fine. It only really affects the first playthrough anyways, beyond that I can appreciate replays just as much as if I hadn't been spoiled in the first place. And I love replaying stuff.