I've always liked the idea of them. I used to rock climb with a gentleman in his late 60's and he used one at the trailhead every weekend. I've actually climbed with quite a few older people, including an former instructor in his 70's that could still out climb most people half his age!, myself included. Guess it all depends on your condition on whether or not you could comfortably get in and out. I'm only 35 and with the Lyme it would be a bit more difficult than it should, but I have no doubt I could.
I am surprised you don't see more families use them. A van and a roof top tent for the kids seems like an ideal combo. I like the hardtop ones that just crank up, takes all of a minute to set it up, but they command a hefty price. Throwing one on a trailer as optimistic mentioned sounds like a good idea and I agree, seems a lot better than sleeping in a small car.
They are just another option full of pros and cons like everything else. For some they are the perfect fit and others their worst nightmare and somewhere in between for everybody else.