I still get about 35 MPG out of my sedan. Average lately has been around 33-34 because I'm doing 70-75 on the highway most of the time. (When I was in college my commute was all state highway surface roads, so by creatively exploiting the shift points it could coast around in fourth gear at 2000 RPM at 45 MPH. Doing that pushed 40 MPG in the summer.) I really wish it was a 5 speed now, though. Running at 3500 RPM to keep up with traffic at 70 downhill is depressing.
No engine or aero mods, unless you count swapping the clogged original EGR valve with a stock replacement.
The fun comes in the corners. For example, an SUV tailgating me is taking the same ramp as I am, and they're simply judging their speed based on mine. I go into the ramp too hot for the SUV to handle, suddenly their front end dips down as they brake and barely stay on the pavement. They left plenty of room after that. Trolling can be fun too. BMW M3 bro keeps flashing his lights at me because I'm only doing 75? Time to engage Grandpa Mode. Some idiot parallelling the rear quarter panel as I'm trying to merge over? Let off the gas until they realize they're doing 40 and get all pissed off and step on it. Some jackass in an Infiniti keeps racing between the lights? Okay. Let him take off as fast as he can, then while he's waiting at the light I'm still coming. Light turns green, he stomps on it to get going and I just give it a bit more gas to get away again. Lather rinse repeat until the Infiniti gets so pissed off they do a ricer flyby and blow the next light.
* How much of a difference will a clay bar make on a plastic car? Let's find out this summer!