Mentioned already, but winglets basically reduced induced drag in a similar manner to more span. In fact, with winglets, you have to cant them so the "lift" is inward, and you end up loading the spar the same as if you'd just made them stick out horizontally -- but also already mentioned, winglets mean that the plane fits in more hangers, terminals, etc.
I think that you'd find that winglets have roughly the same effect as high-aspect ratio wings -- less induced drag, so more windup in maneuvers. You may not have more sensitivity to asymmetric turbulence trying to roll the plane, but you may have more sensitivity to cross wind. To really get all the benefits, you'd need to extend the flap out to the wingtip, with an articulated mechanical nightmare joint, and you might need a degree in aerospace to get the correct relationship between the tip flap and the 'real' flap.
I'm with building a test plane that allows bolt-on wingtips. Then make sure to fly it in bad conditions as well as good. You may need to start with something that flies better than a Twister, like your backup plane's backup plane, or an Imitation, or a known-good ARF from Brodak, or whatever.