16 years is a long time. You must have been doing something right all these years. So give yourself credit for that. With that in mind, I would not worry about the buffets. Do what you do and make sure you are continuing to do it well. Decline in business could be from a number of factors, not just the buffets. Start by taking an honest assessment of your place. After sixteen years, perhaps the dining room could use some freshening up. Does the front of the building and your restaurant look well maintained and inviting? Is the service everything it could be? Has the food begun to slip in quality? Identify where you tell yourself, "Well, that could be better but it isn't important", Those are areas you should be addressing. A useful technique is to play being a customer in your own place from entering to having dinner all the way through to driving out of the parking lot. As you do so, write down any negatives you notice. Do this with the full knowledge of the staff so everyone is on board with the improvement effort. "That's the way we've always done it" is not constructive thinking. Best of all, doing this costs you nothing except your pride and may have tremendous returns.
Here in upstate NY the prevailing attitude supports alot of the buffet mentality. But those individuals who stand out do so by providing a quality experience from start to finish and there are more than enough customers to support them. Best of luck.