Hello all. If it is any help, I have an unlimited data plan on my mobile phone, and use a few apps while on the go with it. I sometimes use BBC Sounds And the RTE Radio Player with it, just under the dashboard in the car, and while on the move, I do get a cupla dropouts on these while driving,but usually very temporary.
I also use Spotify with it and I think that it is fair to say that I have never had a dropout on it at all.
From my own experience, if you already have a good data plan on your existing phone, and only really want to listen to music, there will be no need to get a specific Wifi setup in your car.
Cannot really comment on other apps as I have never used this while driving.