We seem to have a very similar view on what makes our national parks great. I’ve been thinking about a little road trip to a few of them, would you mind sharing your favorites?
Rocky Mountain. I went just as the first snow was rolling in, and think this is a great place off season. Gets busy with better weather though from what I understand. YMMV.
Redwood. Not as wild, but great hikes in solitude and not crowded.
Olympic. The sheer scale of this place is incredible, and again the diversity is amazing.
I really wanted to go to Lassen Volcanic and North Cascades, which I believe will be similar, but weather and timing were not on my side.
Great Basin has a good hike to the peak, a cave system with guided tours, a nice (summertime) campground, and hiking trails to a really impressive arch.
Mt Lassen has a bunch of hikes, geothermal activity, lakes for swimming, a bunch of campgrounds, and some low-frills cabins.
Arches is always way busier than Canyonlands, but there's also a ton of non-NP features around Moab that are even less trafficked. Natural Bridges National Monument is also great. The Notom-Bullfrom road in Capitol Reef is a beautiful drive, and the campground out there is no-amenity, low-traffic.
Sand Dunes, in Colorado, is super cool, with hundred-foot-high sand dunes, but probably only 1-2 days worth of stuff to do in the park itself.
But if you want beautiful scenery without a lot of people, skip the national parks and look for the national forests. (Or sites in the National Park System that aren't National Parks, like National Monuments etc).