As Podge said people win without classes. Also win with classes. I really beleive it's up to you what you get out of the classes. If you can't cook decent BBQ now then most of the classes mentioned here won't help you that much but if you can compete and get some calls now then these classes will improve your results. How much depends on how you can translate what is taught into what you do. These classes won't be something you follow step by step but rather like Dallas says it's some things you take away from each class and add to your own style.
My results improved after taking classes by DR BBQ, Mike and Debbie Davis and Rod and Johnny in one year. In 2003 I took classes by Paul Kirk and USA Smoke and while I learned a lot I didn't know enough about competition to really apply what I learned then
Retired competition cook. BBQ mentor.