Road trips are great. A few years ago, we loaded up and headed into Oklahoma, did Turner Falls, OKC, Toy Museum (this one is FUN), Horseback riding, Hiking etc.
The key to a great road trip is NOT trying to plan every second of the trip. Have some definite targets, but leave yourself some flexibility and enough time to jump off the highway and follow a sign for a local attraction that looks interesting.
There are a ton of things that are off the beaten path and end up being a lot of fun. You don't HAVE to do a theme park or even some of the "normal" destination tourist traps.