There's a reason the national parks are so crowded - especially in the summer. They are unique and one-of-a-kind.
I agree, our parks are getting 'loved to death' - too many people but that's for another post.
There are plenty of wonderful national forest campgrounds surrounding the parks if you want a little more quiet atmosphere but don't expect to go to the popular places and expect no crowds. Colorado has some great small towns and areas to explore. I think those might be for you. Some are Buena Vista, Leadville, Gunninson, Silverton, Pagosa Springs, South Fork, Lake City, Ouray.
I'd suggest spending a few days on the west side of Rocky Mtn. Nat'l Park at Grand Lake and doing a day trip on Trail Ridge Rd. and perhaps work in a nice hike. Then you can see what it's all about without dealing with all the crowds for days. Yes, the beetles have ruined much of the forest on the west side but there are still lovely places to explore.
Good luck finding your spot in Colorado. They're out there!