How much of AlphaGo's success is due to novelty?
I would argue that AlphaGo's advantage cannot be significantly attributed to the novelty of its moves.

The original public AlphaGo games were those against Lee Sedol, the second ranked player in the world, in March 2016. At that time, as mentioned, several of AlphaGo's moves were novel, and surprising to Lee Sedol and observers.

Then, after players had had nine months to study AlphaGo's play style, in December 2016 it played 59 unofficial online games under the names "Magister" and "Master", including against several of the top ranked players. It won every game. I haven't seen much commentary of those games, but my understanding is that some of the players used moves that had first been observed in the original AlphaGo games. So, at this point I think they were less novel, because they were becoming parts of human players' strategies.

Finally, in May 2017, AlphaGo played a variety of games in the Wuzhen Future of Go Summit, including a match against Ke Jie, the top ranked player in the world. The commentary of those games did not indicate that AlphaGo made a significant number of surprising or difficult-to-answer moves, but rather that its sizeable advantage came from its ability to accurately determine the values of moves, trades, and territory, and its ability to play across the whole board instead of concentrating too much on the currently active area.