We flew in on the Friday before Thanksgiving and immigration lines were out to the ramp. It only took about 30 minutes as that had enough staff to handle the crowds. I don't think it would have been worth the extra money for Club Mobay.
Our biggest problem was we chose to save some money and fly in on the 3:10 flight and we normally get to Mobay about 12:15. The Friday traffic in Mobay, Hopewell and Lucea was horrible at that time of day on a friday afternoon. We will in the future make sure we book the earlier flight.
I immigration lines in Atlanta coming home were much much much worse than the lines in Mobay. We flew home the Monday after Thanksgiving. If you are not a Delta Sky member so you get to go to the front of the line in Atlanta the wait in the immigration line was more than a hour.