The early endplates used materials of that era on wings of that era. The end plates had to be braced and the
overall effect or sum of the reduced induced drag and the increased parasite drag was a negative effect.
Winglets came alive again when Dr. Whitcomb, the same NASA scientist that came up with the area ruled fuselages, began study of bird wings and how some were better fliers than others. Whitcomb then found early studies and did wind tunnel testing and later attached winglets to a KC-135 for actual flight tests. The results were very good but given the choice of new engines or winglets, the USAF opted for the engines.
Some of what you see today are 'pretendlets' which are on the wing as a result of marketing and do not actually reduce the vortex that much. Others are very effective but they are point designs.. ie, where does the airplane spend the most time and so you design the winglet for that regime of flight. This means in other flight regimes, the winglets may actually have only a modest effect if any.
As for the 'endplates' look at the formula 1 racers which have an inverted wing held in place by braces on the end. These winglets create a down-force to nail the racer to the course. Those are the modern endplates.
More here...
http://oea.larc.nasa.gov/PAIS/Concep.../winglets.html
And here you can see the Phillips "Multiplane" which used very high aspect ratio airfoils with 'endplates'.
http://www.aerospaceweb.org/question...ry/q0232.shtml
As you can see, it took a while to get the concept to a working tool.