Re: Lot of money....
"Gaffer tape and a hammer is all you need. :-D"
"Dohickey" is now a 30£ bluetooth plug plugging into a standard diag port and a matching Android app (funnily enough one of the higest rated and most popular non-game apps on the Android market).
Worth to have if you go somewhere far out. I am definitely going to get one before my next 5k miles around the Europe road trip (I had some scares with both vehicles lighting up diag on previous occasions).
Coming back to the PC topic - I still build my own to this day and I still repair all of the faults on them (even on laptops) so maintainability is fairly high on my list. I will buy a well built machine which is good value for the money like the HP shoebox (Proliant microserver). Something that is maintainable and well designed.
All in one? Forget it. Shite resolution all of them (except Apple and Dell), priced at 40% premium of a monitor + separate box, overheating laptop parts, wrong choice of disk for a desktop (can I have a decent size hybrid drive please), you name it. Most importantly all on the list are not particularly maintainable (if memory serves me right the HP may be an exemption though, I recall it nicely falling appart for maintenance).