It's been a while since I've written on car computing — over two years, it seems — but that doesn't mean I've stopped thinking about it. The top reasons I would've wanted one in years past would've been for Entertainment and Communication, and I think everyone would agree that today, it's far better to just carry a smartphone than to embed one into your car. And, seeing how smartphones are changing so much so fast, doing more than adding the ability to interface with Bluetooth and/or USB to your vehicle seems silly, at least in short-term.
Navigation doesn't fare too much better, so although it's a toss-up whether dedicated units like Garmin and TomTom are better than smartphone navigation like Google Maps, both are accepted as better (more current maps, better interfaces) than in-dash choices.
I think the use that is least considered is recording. Dash cams are common in Russia because they're used for legal protection, but have given YouTube a great catalog of amazing video. I think there's reason beyond "Hold my beer and watch this" for Americans to have dash cams, and I do want one.
But, ultimately, I think the best reason to get into "Carputers" is Diagnostics, getting into the data that is available from your car's OBDII port. The obvious way is to use an OBDII-to-Bluetooth adapter like the ELM327 or Garmin EcoRoute, but it strikes me that there are enough security vectors in to the New Car that adding more is not a wise route. So, I'm thinking that the Raspberry Pi and an OBDII USB cable might be the better way to handle it, except I'm not sure how to export the data, and while it would be useful to keep track while driving, ultimately, off-the-road analysis is where the usefulness of the process comes in.
I'm thinking that a Raspberry Pi, a cable, a small monitor with composite video and maybe a few other things could be easily turned into a car-monitoring system, and I could pretty easily set something up to only sync with my home network when it's close. I'm not sure whether that's more cost-effective than just getting an ELM327 and an ELM327 app from the Play Store, but I think I'd end up learning more that way.
Anyway, I'm still undecided on the phone/Pi issue, but I think this is something I need to do.