Resort dining is a strange thing. Restaurants depend on a regular flow of customers to survive, and unfortunately, that is only guaranteed during the 3 or so months of the summer season. Off-season dining has to appeal to as many people, and to as wide a cross-section of tastes as possible, or the restaurants will fail.
Good news, however! As of mid-2017 we now have Indigo Indian restaurant on the ocean block of Rehoboth Avenue in Rehoboth, and Minh's Bistro Vietnamese restaurant at Rt. 24 and Coastal Highway. So things are looking up.
Lily Thai does a pretty good job and they are open all season. They survive on a very good lunch special. Confucius is another place that does a consistently good business with upscale Chinese food. They also offer a Sunday dim-sum brunch that is quite popular.
Saketumi, Cultured Pearl and Stingray also survive year-round with good “locals' specials” and a fairly diverse menu. Note that you can get tasty Middle-Eastern items at Semra's Mediterranean Grill on Rehoboth Avenue. Semra's stays open year-round.
The silver lining is that New York, Philadelphia, Baltimore and D.C. are not that far away, and all are meccas for good ethnic dining.