The STi spoiler flexes in the top center at speed like the highway, you can't really see it yourself while driving but my friends have said they notice it driving behind me, it doesn't have to do with damage mounts. What mount? It bolts directly into the trunk Lol. With a ton of studs and nuts, I don't see how that can make the wing have flex...
And the stiffis would stop it from "bouncing" or flexing, because the flexing would cause inconsistencies in airflow at higher speeds. At least that's my theory on them. As for whether they look cool is up to your preference.. I'd bet 90% of the buyers get them for looks anyways.
1990 Civic time-attack project
1990 Toyota Hilux - daily