I agree with Hughver to keep both. The 1-piece is not expensive so it's worth it to improve the smoking performance.
The problem with the 2-piece in the DC is it compromised the performance as a smoker - the 2-piece simply runs too hot (as well as too many hot spots) for even low and slow cooking. It seems to me that the 2-piece works much better in the Jim Bowie and Daniel Boone as they are larger with more and better airflow. But, in the DC, space is limited and the food is (at grate level) closer to the firepot, making the 2-piece problematic.
I've really wanted to like my DC and I don't expect it to smoke like my Mak 1-star, but I do expect it be able to smoke a rack of ribs low and slow without burning them because of excessive heat from the bottom. Now that I've got the 1-piece and used it a few times, I can definitively say that the hot spots and unintended searing/burning have disappeared. Smoking performance has evened out significantly and the DC is working as a good smoker now.
So, if you want to grill, keep the 2-piece. If you want to make this a better smoker, get the 1-piece.