Huge fan of the wireless remote for kiting. I like the idea of strapping the remote to the bar. I strap it to my wrist. Use to let the camera run until it ran out of juice, but discovered my computer could not handle the huge files when it came time to edit. Keeping the clips to 2-3 minutes is a workaround for not having to purchase a $1500 laptop to edit your footage. This works out great for me as well as I kite in waves, and that covers a wave ride and then some.
Can't speak your basic question about the value of purchasing the 3+, but when it comes time to upload your video to Youtube or Vimeo, both cameras offer way more resolution than those platforms can handle. I prefer Vimeo overall for uploading for a variety of factors, which basically boils down to the quality and accessibility of the final product online. You are limited to 1080p at 30fps on Vimeo, and I believe 720p at 30fps on Youtube. If you film at higher rates, it gets compressed and looks like shit. Both cameras are capable of 4kp and 120fps-you get the idea.
Where to mount your camera? Backpack mount is good, but the best, imho, is the line mount, with the camrig. Camrig vids and shots are not only dope for showcasing how epically awesome your kiting skills are, but they are great for training-in other words for seeing how you look and understanding what you need to do to improve. Just an image taken with a camrig mounted gopro i found online. http://camrig.com/gopro-hero3-line-mount