I have read through this post and find many of the concerns interesting, but the mitigation strategies seem excessive as standard drives and hardware work very well in vehicles. I have been running a PC instal in my 60 and later in my 80 Sereis for over 10 years now. Interestingly I only installed surplus machines ( small form factor PC's ) and have never had a drive failure. ( I once left my office laptop in the vehicle at -25C ) the Laptop would not boot. At these temps the car PC would growl and screem a bit until the heat set in, but these generic boxes always booted. My instal consisted of a Touch mouse on steering colum, Wireless micro form factor keyboard, 12 Inch monitor on custom built stand, PC under seat in 60, and straped to rear quater pannel above wheel in HDJ 81 ( 80 sereis).
This is has also always been iterfaced to a GArmin GPS, a USB internet stick , and running nroute/and goole earth software. One hurdle was audio noise from the power inverters and ground loops between the car stereo sys. This was rectified by putting in a two ( stereo ) audio trasformers to DC isolate the audio path between PC and Radio. The Cell data conection is great for listening to millions of radio channels, police /air/fire radio etc.
I also have a tough book I have tried to instal in my BJ 74, but am finding it more dificult than the PC installs. I am thinking of simply useing a Samsung Android phone for this one, its probably more powerfull with a 1 Ghz processor than the PC I put in the 60 10 years ago. ! ( and I can tether its 3G connection to my laptop as needed)
So for anyone considering a car PC, dont hesitate, they are great, put your money on the monitor and mount, for everything else, surplus PC's are great, rarely do you need the high speed and power of a late model PC.