The first hardware upgrade is either a ScanGauge or UltraGauge. Even before it's properly calibrated, the instant mpg numbers are useful- you can watch the effects of other traffic on you.
It's not Nascar or anything and tailgating is an entirely different ball game, but having a car in front and/or behind you helps your aero. As long as things are moving smoothly, you're getting an aero benefit just by being in traffic. Here it's called the
corridor effect.