[ecomodded]

Why put them in front of the windshield on the blue wagon? they are placed right at the low pressure zone before the windshield. If any effect is wanted from them they should of been placed further ahead where the air flow is stronger for them to interact in. To be honest the hood needs a cowling to direct the air away from the windshield not to it.
On the rear VG's appear to be in the air stream with no real purpose. They are not attaching the airflow nor directing it anywhere.
They become Hood Ornaments in the wrong hands.

Its all about placement, first you have to understand how they will interact with the airflow then how you can use that to your cars benefit.
Smoke testing would be a effective way to test the effect of the placement.