I used an iPhone clipped to my p/s visor for awhile and it worked very well. You can run a USB charger to your center console for constant power but maybe bring something to events to download video depending on the drive size of your phone. I think the audio was even better than my Hero3, despite theyre revamping of it, but I havent tried any external mics yet.
The Hero video is super high quality though and the default lens setting is wide angle without too much fisheye, so you can run one forward, one rear to capture close to 360 degrees in HD. plus you can use one remote or a smart phone to control them, including simultaneous pictures/video. I run theyre car charger, which has two USB ports, so you can run two cameras off of it. (Im currently using the second just for remote charging until I get a second camera.)
For the price, I think the Hero3 is a great in-car video solution IMO, so Id personally save up.