Very mixed feelings on this, as a recent entrant to the Alexa world.
On the one hand it is useful. Adding things to a shopping list by voice immediately something's used up is actually very useful, as is the ability to set timers and alarms by voice. OK, there are plenty of other ways of doing that but I do use it. I've also set it up to turn some of my lights on via Lightwave, which is really fun and more useful than it might first seem.
But there are two problems with Alexa. Firstly, it's extremely basic in its functionality. You can add things to a list and review things on a list but not change or process them. Other things like news and jokes are just fluff - unimportant. The second thing is probably worse. Its voice recognition is terrible. For commands it knows it's pretty accurate - near 100%. For simple shopping list items it's pretty good - probably around 80% accuracy. But for to-do list items it is appalling. If it gets one entry in ten right I reckon I'm doing well. So in summary Alexa could be good in a few years' time if they make a lot of progress on the core.
As to Alexa in the car, that is quite possible now. The Dot is physically nobtrusive. It's powered by a USB cable, connection available in most modern cars. For a network, just activate the wireless hotspot on your phone. Job done.