I have looked into this a lot, trying to find a 7" tablet with at least ICS, GPS & BT has been a struggle. The Nexus 7 ticks almost all the boxes and no it wouldn't need removing from the screen just maybe the case depending on how flush the screen is to it... then how trick it is to hardwire and fit a button to replicate power on/off and reset.... only other thing is that it only has the home screen in portrait mode and no SD slot but rooting would sort both out I am sure
I have always though a tablet was a little ott in the cubby as i would never play games, audio is on my 7" dd unit so really just GPS and a link to my odbII dongle.... But a cheap option like a nexus could sway me also having 3/4 free GOS software options is tempting, tried copilot on my xoom and quite impressed, just got to crack iGo