On my Mon-Fri commute (~30 miles round trip, all highway) I tend to drive "normally", which is cruising at 75-80 MPH here in San Diego. However, on the weekends, I drive the piss out of my car.
No point in driving your car like an old lady just so you can trade it in and have the next guy get a great deal and beat the hell out of it. BUT, also no reason to treat the car like shit.