Well it more or less depends on if you want to, or have the need to read license plates, that ability will improve a lot with 60fps, and the video
is more smooth. Of course bitrate does come into play, but not as much I guess. Here are some samples at the bottom of the page, you can tell
there is a huge difference if you do 30fps or 60fps. But the question is do you need it. I would argue that you probably do not need the 60fps,
when are you going to use it ?
I am just getting angry with people saying it makes not difference at all, watch the samples and get the facts straight, it does give you better
video, but IF you need it, THAT is another story !
The thing is like 95 percent of dashcam video is dumped anyway, and if there is a accident or something you can still grab your phone and
take some photos of license plates or whatever you need, you will get better pictures, good angles, and distance. That is something you will
never get with a mounted dashcam in the car.
So the bottom line is, if you get 60fps capability from a chip (for free) or is included in all new chips anyway, why should you not have it,
even if you do not use it, it is there, you might need it for some situations, what do I know. Technology evolves, just as way back, people
where arguing, we do not need HDTV. Or we do not need dashcams recording HD. Where are these critics now !
http://www.photographyblog.com/reviews/sony_a5100_review/sample_images/
End note, another thing that has huge impact is vibrations, having a vibration free mounting (like on radio controlled aircraft that have mounted cameras) will make a huge difference to the video as well. Plus digital image stabilization that all new chips have.