Brining or marinating will definitely add a different flavor dimension to your pork. Some heritage breeds (Berkshire, Mangalitsa, etc.) are flavorful enough to stand on their own without needing enhancement beyond a good rub.
I'd recommend you also consider injection ... especially on short notice this will give you a very reasonable and flavorful alternative. To that end, using a water pan in the smoker chamber with apple juice, beer or other flavorful liquid can also enhance the moisture level of unbrined/unmarinated pork shoulder.
