Since you have no stated reserved plans beyond July 18/19, here's some suggestions:
Leaving RMNP, take CO 7 (the Peak to Peak Highway) out of Estes Park towards Allenspark and Nederland. At the intersection with Co 72, make a right and continue on the Peak to Peak Highway. Besides some great scenery, it's not a difficult drive and it will get you to your next destination -- the Pawnee Campground in the Indian Peaks Wilderness.
H E R E is information for the CG. It's all first come/first serve and since you're arriving on a Thursday, you shouldn't have a problem finding a spot. At Pawnee, there's the incredibly beautiful Brainard Lake, and multiple trails for hiking further back in the Indian Peaks area. Blue Lake is particularly striking in it's beauty and will rival any other location in Colorado for beauty. Several other trails in the area, and if you're truly adventurous, there's several pass trails that you can do in that same area. At 10,600 feet, it will get cold at night, and will be pleasant during the day. There actually may still be some snow in the CG, it doesn't open until the first week of July each year. You WILL be dry camping here, though there is a water fill available, and there's a dump station at the Camp Dick/Peaceful Valley CG.
In the unlikely event that it is full on a Thursday, you can simply backtrack a few miles to either Camp Dick/Peaceful Valley CG, or Olive Ridge CG, which are both right off the Peak to Peak Highway.
H E R E for all 3 campgrounds. There's also good hiking from all 3 of these CGs and at Peaceful Valley there's a nice 4x4 trail for your Jeep.
If you get a spot at Pawnee, consider staying until Sunday. For a day trip, you could plan on continuing touring on the Peak to Peak, to Nederland and on to Black Hawk/Central City. There's also the funky little town of Ward, that's right at the turn off for Pawnee. Nice place to spend a bit of time. And at the turn off for Pawnee, just before you get there, is a wonderful restaurant -- The Millstone Inn, that's been there forever and serves up some good food. It's where the locals go, so you could also meet some very colourful folks from Ward.
If you wanted to spend more time in relative peace and quiet, consider some of the other northern Colorado areas, such as the Poudre Canyon (CO 14) between Laporte and Walden CO. There's also the area around Red Feather Lakes (Larimer CR 74E off US 287). Both areas have hiking trails and 4x4 trails to explore. The link above for 3 three campgrounds also gets you the CG in these areas. If you arrive during the week, you will have no problem with finding a spot, and the host at each can direct you to the first come/first served spots, so you don't have to move, in case you decide to stay for the weekend (they fill up on weekends). In Poudre Canyon, the Mountain Park CG has electric connections and showers. In Red Feather, the 3 CG up there all offer electric connections and common water available.
Between Rocky and these suggestions, this could certainly fill a couple of weeks of your itinerary. And you'll see an area of Colorado that's just as beautiful as the other areas of Colorado...with less people to contend with.
Others will come along with some great suggestions for other parts of the state, including the Arkansas River Valley area and the SW part of the state, which it sounds like you've already experienced to some degree. Still plenty to see in both those areas.