Sure, let's stick to road cars. So you know, the purpose of bringing up the F1 car was the correlation between downforce and drag. So the drag of a stationary F1 car may not be much, but when air is forcing it down (part of the GTRs superb handling, stability, and track performance) it increases it's grip (downforce). That's the point. More force pushing down takes more force to accelerate or maintain speed.
About road cars, can we stick with reasonable road cars and not multimillion dollar hyper car hybrids with fluctuating aerodynamics that change depending on speeds and conditions? Especially since at certain speeds, the downforce lets up because it will destroy the rear suspension. Or it's used as a rear brake. Either way, factors the Insight and GTR do not deal with.
Unfortunately, I can't find anything on the downforce of a G1 Insight.
Oh, and comparing to somewhat ordinary cars:
Corvette Wind-Tunnel Testing - Is Corvette Styling Just For Looks? - Corvette Fever Magazine - View All Page
Only the C3 was able to actually create downforce. The rest all created lift. Now the Corvette is no GTR (although Car and Driver rates the Vette #1, and GTR #5) it also isn't a Focus. I compared the 2009 model GTR to a 2009 model Corvette, because after the "Black" (or is it a V Spec? I forget what they name them) GTR came out, it started getting more and more downforce. Then the regular GTR essentially was as good as the previous year "Black."