Sluggo said:

Not to beat a dead horse here, but it seems Lucas created the new Vader and Palpatines lines to forshadow the big reveal later in the movie.

EMPEROR: We have a new enemy, the young Rebel who destroyed the Death Star. I have no doubt this boy is the offspring of Anakin Skywalker.
VADER: How is that possible?
EMPEROR: Search your feelings, Lord Vader. You will know it to be true. He could destroy us.

VADER: Obi-Wan never told you what happened to your father.
LUKE: He told me enough! He told me you killed him.
VADER: No. I am your father.
LUKE: No. No. That's not true! That's impossible!
VADER: Search your feelings. You know it to be true.

I think that the idea behind the new dialogue is interesting, but the wording along with Ian's delivery don't make the SE change an improvement to the original.

Beating done.

I agree that it does have nice symmetry, and it would work well, if not for the earlier reveal that Vader is already “obsessed” with Luke. In fact, if you think it about it too hard (which we all clearly have) it starts to seem like the evil Emperor, who meticulously plotted his rise to power, started an intergalactic war to help him along and even (possibly) manipulated the Force into conceiving his own apprentice, has clearly lost a step or two if it takes him three years to find out who blew up his big 20-year long construction project a couple days after it was finished!