I am on the fence about it. On the one hand there are rubs and sauces out there that are both readily available, and proven winners. Part of me wants to go ahead and use them.
On the other hand I look at the future. Look at teams like Quau, Gotta Bull, Smoking Triggers, Pellet Envy, and all the other big names at the top of competition BBQ. They were all newbies getting there butts kicked once too. I know its a long shot, but suppose this really gets in your blood, and you end up being one of this big names. You may decide you want to market your sauce and rub. It won't be easy to do that if you haven't actually developed your own. Plus there is the ego boost of knowing you did it with your own stuff.
Is that a likely possibility? No its not, but it is something to consider. If that is not even on your radar then I would use a concoction of commercial sauces and rubs.