I would choose California Grill. The menu is much more extensive with lots of different options. If by adult dinner you mean that you want a restaurant without children present CG is a better bet too if you request the "wine room."
I haven't been to Narcoossee's but we ate at California Grill about a week ago. My husband had the vegetarian entree and enjoyed it a lot.The view was magical as well.
I am vegetarian too and I ate at both places last year. Definitely go to California Grill ---I got a vegetarian entree---it had all different vegetarian samples ---it was wonderful! I can't wait til May to get it again!