i only see one reason not to include wifi--if you can tether to your internet-enabled phone. i have used it on more then one occasion just to get directions or a address that i forgot at home. if you shop around enough, wifi is too cheap not to include. and if you already pay for it on your phone, get some more use out of it..
i also think that a keyboard is necessary as well. there is only so much you can do on a 7" screen before you start to go crazy trying to use a stylus to type stuff..
but overall, i really haven't used either of those lately in my car-- really just the hdd space for my music. though, i have only driven my car about 10 times in the last 3 mo., so not much opportunity..
and i never fiddle with my carpc while driving, and will not perform tasks outside of the FE while the car is in gear. i always pull into a parking lot, or wait until i'm at home.. it is just not that easy to access windows while rolling..