It's a long way between Mobile and St. Augustine. I'd break it up and see some of the AL/FL gulf coast on one day, and then make a beeline the following day. Wentzell's in Mobile or Point Clear is a good place for some fried gulf seafood. I recommend a stroll through the Grand Hotel at Point Clear. Just tell the guard you're there to eat and he'll let you pass. Stroll under the live oaks on the grounds and then go to bay side and take in the bay view. If you have the money and are there in the evening, skip Wentzell's and eat at the Wash House.
If you're on a budget, Due east of Point Clear about 25 miles is Foley, home of Julio Jones and Robert Lester. If you are in an outlet mood, they're there, but the best thing in Foley (if Julio's not in town) is Lambert's, home of the "throwed roll". It's a big slop the hogs, country cookin' place that serves large yeast rolls, served by a kid throwing them around the rooms. It's quite the spectacle, not too pricey, and you can eat enough there to last two days. Due south of Foley is Gulf Shores and to its east Orange Beach. Lulu's on the intracoastal is Jimmy Buffet's sister's place, Sea N Suds jutting out on the beach in downtown Gulf Shores is good food and fairly cheap, and Doc's in Orange Beach is a good local experience. Of course another five miles east is the FloraBama, not to be missed. As I mentioned earlier, don't miss the Blue Angels if your itinerary accommodates. THEN cut out for the long drive to St. Augustine, and be sure to eat at the Columbian Restaurant in St. Augustine, good spanish/cuban and a landmark.
I'll think some more about other southeast spots, and don't be shy asking questions.
RTR,
Tim