Coco cafe DOES serve a vegetarian buffet on Sundays at the moment, but obviously restaurants sometimes change their menus, so you should check first with the restaurant, especially if you are going weeks or months after the review (this is a non-vegetarian restaurant, after all). Check also if it is lunch or dinner.
The buffet costs (as of June 2013) THB 499 net and is amazing value - Indian, Thai, Chinese and European food, with live Indian music (not too loud in my experience, and I am fussy about that kind of thing - it is a large room and you can sit away from the statge).
We found the quality of the food to be very good, with some stand-out dishes.
Would give 5 stars but this is not allowed for a non-vegetarian restaurant.
Cons: Check first if you're veggie