In the story the biggest lesson we learn is that the only matches who will work in the story (similarly to all of Austen's novels) will be the matches made for love, despite of what others say of what makes a proper or convenient marriage.
The individual couples work out either by love or chance, or perhaps both. But there is not much evidence to suggest that one character affects the behavior of another. There is, however, enough evidence to show how a husband determines the fate of his wife, but not the other way around.
If you take Lady Elliot, for example, she was sensible and sweet. She spend her life living up to the Elliot name and made sure her husband enjoyed the reputation of having a great wife. Did it change his ways? Hardly. He continued his squandering and dandy-ism. He never once stopped to think about his responsibilities with his family. Hence, this match was not made in heaven.
Similarly with the widowed Mrs. Smith, her husband never changed even as she came into his life young, naive, and lovingly. He died after a life of excess that left his wife a destitute.
The union of Wentworth and Anne was fueled by love. We know that she had previously made a choice to leave him, and he was indifferent to her because she hurt him. Yet when they came back together they showed how they tested-and won- against the passing of time. Anne and Wentworth would be one of the few couples that are very alike in character (sort of like Jane and Bingley in Pride and Prejudice) and that is why their relationship works out. Yet, again, one cannot say that in the novel the good and bad characters influence their opposites. They simply match by personality and by chance.