Taking out the dihedral will neither increase lift, nor make for a more efficient wing.

Ok, MAYBE - In some EXTREMELY insignificant amount it might, but you'd need some pretty sensitive equipment to measure it. And you certainly wouldn't be able to notice that difference in flight.

The main porpose of dihedral is to keep the plane stable in its Roll Axis. Remove the dihedral, and the plane will roll better, and fly inverted with less effort, but it won't run faster, or jump higher, or leap through hoops.