Hi Brandon - fellow Civic driver. I have a 2007 EX sedan. I saw potential in blocking the gap between the hood and the grille. I blocked that and the upper grille with styrofoam wrapped in duct tape. (I have a silver one - so that blended in quite nicely.) That improved my warm up time and on the freeway I say some improvement. Now that I drive in the city mostly I decided to go without either to maximize cooling.
I'm assuming you're still running on the OEM tires: Goodyear RS-A or Bridgestone EL400? I had the RS-A - which wore out very quickly - 17,000 miles and they were down to 4-6/32nds or so. Replaced them with Michelin MXV Primacy tires. They are quieter and much more comfortable. Mileage improved slightly. Now I run Bridgestone Turanzas. Excellent wet grip, but a little noisier than the Michelins. I also had Michelin Hydroedge tires on our previous car which were awesome in the rain and still very good in the dry. Not so good in slushy snow.
So what I'm saying is tires make a big difference on my car - maybe yours too.
I do not floor the gas pedal all the way and ease off the throttle as the rpms rise. That way I get better initial acceleration without forcing the ECU to shift away from the economy camshafts. Try shifting at around 2200 rpm so the rpms in the next gear start at 1500-1600.
Oh, and use engine braking am much as you can. I try to make the most of the free revving engine and "free miles" I get from the DFCO (see glossary). I usually downshift to 3rd gear from 60-70, and then 2nd at around 40-44 mph. I try to match the revs by blipping the throttle to minimize wear on the clutch and drivetrain.
My best mileage using the above techniques is 50. 45 mpg (best) when driving 55 and under on highway.
If you feel mod-happy consider turning the license plate bracket in the front around 180 degrees. It requires some cutting of the bracket, but it gives you more blocking of the grille (sorta) and cleans up the look in the front of your car. Thought about doing it when replacing the fog lights (that had chipped the lenses for the THIRD time...

), but I chickened out.
Oh, and consider modifying your route to reduce the number of stoplights. Sometimes driving further but not stopping can actually save you more gas. It avoids wasting the energy it took to get you up to speed in the first place.
Roland