Crash - I have had awesome success with the flat lid, I have two grate levels with a diffuser but because of the distance I have to do Turkeys or pork butts on the lower grate. With a taller lid I could probably run double the butts or cook my turkey on the highest grate.
I guess the next logical question is what would a "good price" be on a used kettle if I have to buy the whole thing? I've tried to weigh the new prices against the cone mod that Fat Charlie runs on his UDS builds