I think it just depends on how you travel and what you do when you get there.
We would travel, park the motorhome for a week or two and do a lot of siteseeing in the surrounding area, many times in a 100-mile radius. A lot of it is done on unpaved roads because that's where the good scenery is located. There are some mountain drives that a RV couldn't do. We might also decide to go out for a meal on a whim. It's much easier to just hop in the car. Going to a national park is a lot easier to tour in a car than finding a parking space for a RV. Parking at a trailhead to do a hike would not have enough space for a RV, in most cases. We love geocaching and you definitely wouldn't do much of that in a RV. It takes you to places you'd never know were there - most often on unpaved gravel roads.
The places we go wouldn't have car rentals available. We like the boonies.
If you're a weekend traveler you could easily do it with a car. If you're traveling the country for an extended time, a car would be necessary for us. I guess it just depends if you do things outside of the campground. We spend very little time in a campground. We're out there to explore.
