You can see this same feature discussed on the Chevrolet Volt as well:
http://ecomodder.com/forum/showthrea...ures-4629.html
BMW and others have been incorporating similar airflow "trip" points to promote clean separation off tail light lenses, which typically have large corner radii.
I'd venture a guess and say this mod would be worth doing to any vehicle where the upstream flow is relatively unturbulent, and the transition at the end of the car has an ample radius.
The 1st gen Insight, with its skirted rear wheels and rounded rear bumper cover corner would be a good candidate.
The only catch is that the effect of this mod is likely so small it wouldn't be easily measurable outside of a wind tunnel or with CFD.