By comparison, I am only a fairly average accountant.

But the main area of my interest (F1A glider) drew me into the area of induced drag many years back.

My argument must be simple, and comparatively brief - so here goes...

What Reg says, I generally agree with except;
[ul][*]The formation of the vortex, the fact that the air is "moved" from lower surface to upper as he describes, requires energy.[*]To the best of my knowledge, that energy does not come out of the surrounding air, it comes from the aircraft itself.[*]The amount of energy "absorbed" by the vortex depends upon the lift coefficient of the wing, its velocity, and the shape of the wing (planform) itself.[*]The planform of the wing relates the "local wing loading" to the "local lift generation". To illustrate - an elliptical wing generates no vortex because the "element loading" always equals the "local lift". A square wing generates a very large vortex because the distribution of loading differs considerably from the distribution of lift across the span.
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(I am doing my best here...)
So, why my interest in induced drag? Because in F1A gliders, it constitutes some 60+% of the total drag budget. Very slow, high lift wings making very large slow vortices.

So I disagree with Reg to this extent - in some model aircraft, and in some 1:1 aircraft as well, induced drag is an important part of the design. HOW important is the real question.

For the general sport power model, I do agree with Reg - it is a relatively small part of the equation.

To the original question, the simplest form of "vortex control" -
[ul][*]Square edge is fine for most sport models[*]Rounded edge adds a little bit of aesthetics perhaps.[*]The Hoerner tip is the first really practical move. [*]Then you can get really fancy with winglets if you want...
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If you are designing your own model, especially for competition purposes, you will get far more result from moving toward an elliptical planform, than from adding any winglets or tips or anything else.

Then you get into the compromises...