I bought my Nexus 7 last July, and keep mine naked -- not even a screen protector to mar the tactile experience Asus worked so hard to achieve.
It's been bulletproof. My wife dumped it out of her purse onto the concrete the other night. The impact on the corner caused the case to separate a bit. Snapped it back together, and it's still perfect.
I've had it for around 180 days now, so I figure I've paid about $1.30/day for it, thus far. I've derived WAY more value from the device than that, so even if it quit dead right now I wouldn't feel ripped off.
Bottom line; Unless you're incredibly rough on things, insurance on a device like the N7 is a sucker's bet.