So my wife and I are going south for this anniversary and we're taking the auto train down to Sanford FL in April. My wife has mentioned St. Augustine, Jekyll Island, Willmington NC and places like that. We've done Savannah and Charleston before, so we were interested in doing something similarly interesting with potential for bicycling.
We like multi use paths and enjoy road biking as long as the traffic ain't heavy, roads have nice shoulders etc. I've done some searches in here and am getting the impression that road biking along the coast can mean traffic.
I can't speak for Wilmington NC because I've never been there. However, I live in Savannah and have lived in St Augustine and near Brunswick (Jekyll). Savannah and St Augustine have both gotten so big that it's tough to do the Rec riding thing with a minimum of traffic. Jekyll seems like your best bet for several reasons.
--Traffic is pretty much non-existent and the island speed limit is ~30mph.
--It's peaceful, warm, sunny and the perimeter road is ~17 miles IIRC.
--There is also golf and a wonderful tennis center if you're into that kind of thing.
--The beach is nice although a little mucky.
--There are a few decent places to eat (Blackbeards, The Club).
--And what I think is the most important reason to spend a vacation at Jekyll. It's a coastal island that is owned by the State of Ga and operates like a State Park. Development is currently limited but there is a push by the legislation and real estate developers to build up the south end of the island to make it more closely resemble places like HH and Myrtle Beach. These things take time but the door is closing for Jekyll to remain the place that it currently is.
Go there and enjoy the peace and quiet before it's turned into a Spring Break headquarters. You will not regret it. If you have the means I recommend staying at the Jekyll Is Club on the Intracoastal side. Go fishing on the pier, walking on the beach, golfing with the deer and play tennis on the clay surrounded by bottle brushes and azaleas. I'm starting to sound like a travel brochure but it's because I really love the place and the things that make me love it are being threatened by development.
Let us know what you decide and how the trip goes. BTW, how many years?