I'm all in favor of splitting California up into two different states because I'm a Democrat.
Right now, California gets two Senators. Both of these Senators figure to be Democrats far into the forseeable future. If California was split into two states then that would mean an additional two Senators would be added to Congress and both of these Senators would be Democrats far into the forseeable future.
This is also the reason California would never be split into two states. There is NO possible way that Republicans would accept another two Democratic Senators being added to Congress. Even if the people of California wanted to split their state in half, such a measure would be fought tooth and nail by those who wish to keep the balance of power as it stands now.
No, California should not be divided into two separate states, because California is a powerhouse at it is. California is a leader among states. People often look to what the California courts do in order to set social policy for the rest of the country. With California so powerful, they should maintain it by staying unified.