I've seen Mac King's show three times now. It hasn't changed at all -- he uses the exact same punchlines, same tricks, and same joke timing. But his show is good enough that it definitely falls into the "If it's not broke, don't fix it" category.
Don't pay full-price for this, though. You can pick up "free" tickets on the Strip (just pay for a slightly overpriced drink). It's an afternoon show so easy to get to.