Does he have remorse?
Does he repent his wrongdoings?
Why does he see ghosts?
Does seeing ghosts mean he has a conscience?
Why does he help needy people?
Because he's basically good, or he wants to make up for his evil acts?
Why does he commit suicide?
Does killing himself mean he's more noble or more cowardly than Raskolnikov?
Or does he kill himself not because of repentance and self-disgust, but only because he can never have Dunya?
Is he the opposite of Raskolnikov, who is innately good, whereas he is innately bad?
Or does he stand for 1 of the 2 opposing forces in Raskolnikov's nature?
Or is he Raskolnikov's doppelgänger?
A few things to note:
1/ If sometimes Raskolnikov shows his compassion by helping people, Svidrigailov also helps people.
2/ Svidrigailov isn't a man of high ideals. He kills because he needs to and wants to (and because he lacks a sense of morality?). He has self-awareness and knows what kind of person he himself is, he doesn't try to appear better and doesn't try to rationalise his crimes.
3/ Even in the end, as seen in the Epilogue, Raskolnikov doesn't repent. It also seems that the whole time he's tormented less by the fact that he kills and it's wrong to kill than by his uncertainty about his theory and whether he belongs to the group of extraordinary men as he thought. While I think it's because of his conscience and remorse that Svidrigailov sees ghosts and later decides to end his life.
4/ It's more difficult for Raskolnikov to change, because the root of the problem is his theory and the fact that he, even in prison, fails to see the faults in his reasoning, his utilitarian thinking.
5/ This might be no more than my personal perception, but, while I can feel that Svidrigailov loves Dunya truly, I fail to see Raskolnikov's love for Sonya. Initially he's drawn to her because he falsely believes that they are similar since both have crossed the line. Later, his feelings for her, the way I see it, are only compassion with some gratitude.
As the novel ends, Raskolnikov's seemingly about to convert.
Will that change him?