OEM Aerodynamic options (to 'S' or not to 'S')

[SpaceShot]

I got a minimally equipped LB 5 speed with manual everything, back in April. Because the cold weather package is mandatory in New England, it came with the 15in wheels. Rather than getting dealer optional gauges consider getting the ScanGuage which can display Tach and a bunch more but also gives instant and average MPG. It doesn't need any tools to install and easily fits in the drivers glove box.

I installed the aftermarket cruise control, but I got more MPG gain from tire pressure, the ScanGuage, and a K&N air filter. (in that order) I use synthetic 0w-30 oil, but the gain is just 0.5-1.0 MPG.
My commute is 60 miles each way and I have done some long vacation trips fully loaded with family and gear. (MPG range 36 - 45)
The only aero mod I am considering is to block the lower grill opening for the cold weather. Around here the roads are too rough to keep any ground effects from getting bashed up.

I do like the seats in my wife's Scion XB better than the Yaris as the side bolstering is better and the seat bottom is not so flat on long trips. I just went to the local PepBoys and got some racing seat covers for $25 that seem to make nearly as comfortable as the XB.