Well destroying Earth would have also altered the story quite a bit. An important component to the story was Spock losing his home and his the emotional conflict he had regarding it. True, his mother was from Earth, but Spock was raised as a Vulcan and grew up on Vulcan. It was pretty much what he knew as home for most of his life. Destroying Earth would have quite an effect on us the audience, but it doesn't really do anything for the story. If anything it takes away from the story.
"Don't confuse facts with reality."
-Robert D. Ballard