I also had a Jeep Grand Cherokee (assassinated last week by an oncoming tire which fell off a trailer going the other way, but that is another story
I didn't use the ACC to avoid watching the traffic in front of me rather to avoid having to constantly override the cruise control because the vehicle in front of wasn't using THEIR cruise control and varied their speed by 10 MPH or so. Also, cruise control is much better than me to remember not to exceed my target speed.
Living in Idaho, it is often 100 miles or more between towns and my foot tends to get heavier.
That said, I too would like to be able to set the following distance to more than the Jeep currently allows.