You're right, for flashing tunes etc. wireless OBDII isn't an option. For gauges, it would work fine. I needed something that allowed flashing and gauges, hence the cable option. Also, I just switched (again) to an iPhone, so I had the luxury of having a really nice Android (6 GB RAM) to use for this project.
As far as charging, the biggest power draw is going to be the display (if you keep the phone on airplane mode, which you should). On a 5+ hr drive this week I only used ~30% battery. So for my uses, charging separately works fine.
Also, I had some rather spirited drives through some back roads, some poorly maintained, on the trip and after hitting a dip/hole at speeds I shouldn't divulge I was pleasantly surprised that the phone didn't move. Since it is a secondary phone that doesn't support wireless charging, I was able to put 2 relatively thick steel plates on the back w/ 3M adhesive. These nearly cover the entire rear surface and definitely help the phone stay in place during spirited/track driving. Honestly my brakes were fading before the phone would ever move
