Yes you do earn AP for repairing walls and doors. I "think" you do for siege engines as well, though that is likely only for siege engines belonging to other members of you alliance.

However, I have never tested to see how many points you get for those tasks, but I have seen it stated many times that you do, and that matches with my experience.

Pretty much anything you do to serve the greater cause, whether its by combat or combat support, earns you AP.