My niece got married at the beach this spring and wore a fairly dressy, beautiful and very fitted mermaid dress. She did wear shoes walking down the boardwalk to the beach, then took them off to walk down the aisle on the beach, put them back on for the reception. The bridesmaids wore cocktail length dark turqoise sundresses. The men (including groom) all wore khaki-colored linen pants with white linen shirts. Oh, and the entire wedding party came down the aisle wearing sunglasses. It was classy and fun, all at the same time.
Edited to add: they did not have a runner, her dress was long, and wasn't dirty or destroyed at all by being on the beach. Now, if it's raining and it gets wet, then if might get dirty, which could happen at anyone's wedding.