Most Cracker Barrel restaurants are usually located along interstate highways and are usually busy. That's the reason I don't go to them. I've never been in one that wasn't busy and have never gotten prompt service in one.
I suspect the one at Murrells Inlet is normally crowded and being at the beach, a lot of people are living on 'island time', including the wait staff, so a 30 minute wait is probably not unusual, regardless of the color of the customer.