Hi Neil,
Yes I have noticed same thing about temprature. I never saw red coolant temprature light came on ever. I use software called OBDScope
OBDScope - The OBD tool for Symbian on my Nokia E71. It does all things what Scanguage or Ultra gauge does and it was only $10 bucks. I bought the Bluetooth OBD reader off eBay for only $20.
I do not have the slot just below the front grill like you have. Only two front grill slots and those I can block with black tape. I do have part of the lower front grill blocked.
Mooneyes hub caps have helped a little like 1MPG improvement. I would definitely go ahead and create those wheel skirts as soon as possible. Lowering vehicle with new springs looks expensive so I will not go there.
I do not have any mud flaps at all. The rear bumper looks like parachute and blocking that will help a lot I think. I will keep posting my findings.
K&N filter is nice but did not see much improvements on the MPGs.
Also this week I am using Cruise as much as possible for the most of the stretch of the drive to figure out taking off right foot will improve anthing or not.
Thanks