I really think it depends on the car, and the cars main purpose.
I'm running 10.1 @ 137 right now, and even when I dip into the 9s I'm not going to cage it. I drive the car on the street all the time, and frequently have my kids in it. To me, a 9.99 cage on the street is more dangerous than the few 9.x @ 14x passes I will click off 2 or 3 days a year uncaged (in this car). But this is an AWD car with 6 air bags.
If I had a 9 second fox body... it just wouldn't be a street car, and I would have an appropriate cage. My Cobra trapped 130 (didn't ET for shit though) and it didn't feel "safe" to me going down the track. Losing traction at half track or beyond, with RWD car, built to OLD NHTSA safety specs can turn ugly real quick.