Honestly, I don't think I've had any issues vs. Necrons for a very long time.
AV13 vehicles don't really mean anything to us because of the # of Dark Lances we have in the army. As long as you play well with cover and utilize your longer range, you'll be just fine.
I think what players need is:
-A strong presentation of Dark Lances.
-Both Warriors and Wyches in their army.
-Careful assault techniques so you don't get your important characters MSS'd.
-And bring one of your fliers; both the Voidraven and Razorwing are excellent vs. Necrons due to their air-to-ground missiles.