The '09 grille is no different than '07 grille. How much loss of benefit is there between completely blocking the grille from the front vs. the rear vs. not at all? Is there still enough air circulation from under the car to keep the engine cool?
I like this in general because it does not seem terribly complicated.
Grille blocking differs from one car to the next. On both my VW and my GMC, I could block off 100% of the radiator or the grille and the engine temperature was not affected (but the GMC's automatic transmission fluid temperature went way up).
User maximilian talked about grille blocking with his Accent here: http://www.gassavers.org/showthread.php?t=10437
You might want to post in his thread asking if he ever did it and how it affected his temperature. He did try taping off the entire upper grille and did not experience any temperature increase, but the lower grille is probably where most of your cooling and aerodynamic drag comes from.
As for the ScanGauge, if you've got some kind of fuel rate or fuel economy display then it might not pay for itself. It's a great tool and a great toy for anyone interested in cars. Some of its other functions can be had less expensively (a code scanner/clearer and a hacky DIY fuel rate meter can be had for investments of $40/each). If you don't have any realtime fuel economy or fuel rate display then it will easily pay for itself by teaching you about your car and your roads.