When EK got the 300 ER's one of the test pilots gave us a brief on the aircraft and was asked this question.
Answer
The raked wing tips give the required performance increase with only limited additional wieght in the wing structure.
Also and I quote " To get the same performance increase, the wing-lets would have to be 21 Ft. High with a corresponding huge increase in the wing wieght to support".
Horse's for courses ??