The most effective tool for improving your barbecue contest results is a a digital camera. Forget about the secret rubs and sauces and all the time wasting and money wasting gadgets for sale. If the best barbecue in the world doesn't look good in a turn-in box, it's probably not going to win 1st place.
The Canon Powershot at the left costs less than $260 at Amazon and can be purchased at Wal-Mart and Target too. Linda and I have taken a lot of bbq pictures with it.
If you are not already doing it, take a picture of your turn-in boxes just before you close the lid. When the box is opened for judging, that picture is what they're going to see. After you get your results from the event, whether they are positive or negative, the digital picture can help you make adjustments for the next event. You can download the pictures to you computer at home and then you'll have the entire season of turn-in boxes for reference later. Over a period of three or four contests, I am sure the camera will provide you with ideas to improve your appearance scores and win more prize money.
A digital camera can also help you with your at home practicing. Get some boxes and practice setting up boxes when you do your practice cooks. Take pictures of them and compare them with your next practice cook or to your next contest boxes. I promise it works.
Here's a picture of a first place brisket box.
If you're looking for an all around top of the line point and shoot camera, consider the Panasonic FZ50.