Shep -
Just a warning, I-95 is undegoing widening to six lanes the entire length of St Johns County (where St. Augustine is), about 30 miles. Traffic still moves pretty well, but the road is narrow, & you have to really keep your eyes open.
If you stop at St. Augustine, the SR 16 exit has a Belz Factory Outlet Mall with a "Character Premier" Disney outlet in it.
If oyu go to the beach, the SR 207 exit (5 miles south of SR 16) will take you east to SR 312, which will take you straight to the beach. It has just undergone a 2 year, multi-gazillion $$$ restoration, so it's nice and wide. The state park is foot traffic only on the beach, and St. augustine Beach is open for driving, but is well controlled and safe.
Stop in, Spend money, Have fun!!!