Jim,
From all that I've read, brining helps to add juciness to the bird. The same as injecting and the same as buying an "enhanced" bird. So you can just buy an "enhanced" bird and not brine or inject and you'll still get a juicy end product. I think there would be no reason to inject an "enhanced" bird since it already has the salt solution in it. On the bird I cooked a few weeks ago, I brined it and it was "enhanced" as well so I cut the salt in the brine in half. Did the brine make it better since it was "enhanced"? I really don't know, but I feel it didn't hurt. I also let it sit in the fridge for 12-14 hours to "dry" it out and the skin did turn out crispy, which is why I dried it. Plus, I also rubbed the the skin with olive oil to help with the crispiness as well. Hope this helps.
Tim