But we keep on having this "opposite poles attract each other" kind of narrative in books and movies. I guess that two people agreeing on almost everything from the get-go makes for really boring stories.
This depends on how you define "personality" and "values". Because for example, according to psychological research, personality traits (as defined by the Big 5 model of personality) are strongly correlated with things such as political beliefs (which could be argued is a subset of a person's values at least), and are largely stable over time. So it wouldn't be too much of a stretch to suggest that the more similar the personalities between a couple, the higher the probability of them also having a large set of overlapping "values", however you choose to define them.
Not every point of disagreement is important: not every value has relevance to a family and not every value one holds is equally difficult to compromise. It's more important to agree on things like finances, children, moral/ethical standpoints, etc... than on politics, music, or hobbies and interests.