I have always been told the upturned wingtips, blended or otherwise, were to reduce the tip votex's and thereby reduce drag, not to increase lift.

And on the gliders, again, it would be too heavy to build a stiff wing that didn't bend at all. If you build it light, it will bend. I don't see how the bent up wings can increase lift in the vertical, as lift acts perpendicular to the lifting surface, correct?