TomD- Don't think you're being a wuss, I just think you're assuming I am. Believe me, I'm well aware how long the drive is. I've driven to California, Wyoming, and all up and down the east coast. Driving is not really an issue for me, though I definitely don't want it to dominate my trip. That being said, I am going to scale it down quite a bit. That seems to be the overwhelming advice I'm getting.

So, my revised route is looking something like this:
Mammoth cave
Buffalo river
Big bend
Guadalupe mountains
Carlsbad caverns
Grand Canyon
Zion
Capitol reef
Canyonlands
Grand Teton
Yellowstone
Isle royale

I think that's a little more reasonable in terms of driving hours. There's a bit of a gap between canyonlands and teton, but I kind of assumed I could easily find good camping spots on the way. Look forward to hearing some more feedback from everyone!