Indeed, if "we can be sure that 4 stories are definitely better spoilered", there's no need to statistically test the nil hypothesis because we already have definite evidence that it is false!

Okay, if all you're testing is that "there exist stories for which spoilers make reading more fun" then yes, you're done at that point. As far as I'm concerned, it's obvious that such stories exist for either direction; the conclusion "spoilers are good" or "spoilers are bad" follows if one type of story dominates.