Charlie,

 

I thought that a winglet was equivalent to a wing extension - the benefit (beyond the change in aspect ratio) was that the wing didn't have to actually be longer (read stronger, too) and the winglet would have lower drag than the extension because tip vortices were reduced.  Of course, that meant that there would be greater drag than the wing without either the extension or the winglet.  Perhaps the IVP wing should have been shortened if winglets were to be utilized. 

 

I just read a short and interesting discussion of winglets at

 

 

It also noted that careful design and testing would be required.