Jon,
I yield to others with more experience at N Berwick than I. I have only played there twice, once with the wind into my face on 18 and once downwind. I have not played 18 with a crosswind toward the carpark.
Into the wind, I hit driver short and left of the green. The pitch was straightforward. Downwind I drove the left front of the green.
In neither case did I feel threatened by the OB. I am not a particularly long hitter (250-260 with a good tee shot), but I am (usually) pretty straight off the tee. And my miss is more likely to be left than right.
I wish I had played shots from short and right of the green just to get a feel for the difficulty. I can see how the approach would be more difficult than from the left. But it did not look that difficult. My impression was that OB is the only real problem.
I agree that in a strong left to right wind, the hole would be very different. A more cautious tee shot would be in order.
Bottom line for me: The questions asked by #18 are not as difficult as those posed by some other holes on the course. BUT I still love the hole for its fabulous setting. And as Ran says in his review of N Berwick, you wouldn't want this wonderful course to end with a conventional par 4. #18 is a fitting punctuation mark for a my favorite course (so far).
(Next time I play N Berwick, I am sure to hit it into the carpark.)