Certainly, if you're truly upset at having been spoiled, that will have an inevitable negative impact on your enjoyment because you quite simply are going into it with negative emotions. As someone who has been spoiled on the ending to Bioshock Infinite but has had a few days now to sort of mull that over, I find I'm still really interested in experiencing the story and seeing how it all leads to the conclusion. Being spoiled, say, the day before release would have probably been rough.
I mainly agree with the portion of the study that says it's likely to be less distracting. Since I already know where the story ends up, I don't have to try to predict plot elements and I can more enjoy the story "in the moment." That's been the case for me in the past with other narratives, especially since I'm the type of person who tends to try to guess what's coming up.