To be honest you have stumbled upon one of the conundrums about having a fully functioning android tablet in the dashboard of your car - what do you actually use it for?
They look great, they produce a decent sound, having a big sat nav display is a big plus, I can see how a reverse parking camera might come in handy too and Torque would be nice (however my Tourer doesn't have OBDII so it was pointless for me) - but I never found a media player that was particularly easy (or safe) to use while driving and, as you have noted, most of the apps in the Play store aren't exactly 'use while driving friendly' or would actually be of any use when you are driving either
In the end you usually end up using them as a radio and sat nav with occasional use as a media player and that's fine - but I did eventually find myself thinking occasionally that I'd paid rather a lot for that
