This is pretty cool! I play with my nexus too much to mount it into my dash, but I like the idea. With both the torque app for diagnostics and plain old navigation, all you would need is the 3g version or wireless tether it to your phone and you'd never have to leave your car!
Also, op, if youre into rooting and stuff like that, you can root the nexus 7 and then be able to download an app (i think the app is stickmount or something similar) and you could use whats called an OTG cable that allows to plug in full size usb peripherals into the n7. The cables usually run like a dollar or two.