Your video got letterboxed because you filmed in 960p, which most editing programs and players don't support (I know Youtube doesn't but I don't know about NS, I assume not.) The black around the edges is automatically added, which will make the picture smaller and not look as good. Try filming in 720 or 1080 and it shouldn't be an issue. You can also get your shots in 960 down to 720 by taking off 120 pixels from the top and bottom (You can use mpeg streamclip for this, it's free to download.)
It's not that hard to make a pole mount out of the mounts GoPro gives you, there's a lot of tutorials and stuff around NS and the internet beyond. It will make follow cams way better, and you can also do some swing cams which are relatively smooth but are more interesting and easier than a using a tripod, especially for lapping. While it would be ideal, it's not always practical to stop for a while to set up a shot.
I don't know which editing program you use and what you're doing your color correcting with, but the overexposed whites are fairly simple to fix with FCP.
Get closer. Gopro shots look best when the subject is less then 30ft away.
I know none of that helps really with the actual editing, but it should help make your shots look better. I think that the best looking parts of your edit were from your helmet shots.
Good luck, it was fun to watch