All my home Pis network boot, so there is no card to fail. You can also change what OS they boot into by just renaming a symlink on the server and rebooting them. Very convenient.
I'm curious what you're using all these Pis for when you've got a server on the network to provide network boot. Can you not just use the device that's providing network boot to provide whatever you're running on the Pis?
No, because the server is in the wrong place. Some Pis are connected to televisions and play videos, or emulated games. One is connected to my hi-fi. One has a GPS receiver on it for NTP. One is a photo frame. Basically, the Pis exist to interface with the real world.
