My 2 cents...
Lift is related to the wing foil used and the surface area of the wing.
An elliptical wing is not needed to increase the surface area or change the wing foil. However....
One of the big culprits of drag in a wing are the wing tips. The elliptical wing is very good at not creating a vortex in the wing tips thus reducing drag.
See
http://en.wikipedia.org/wiki/Wing_tip