I'll try to reserve my asshole-ness here.
of course, I don't know much more about Shane than what I've seen in movies/the media, but I don't think he would have wanted it any other way. look at his attitude and personality... having his ashes spread in the mountains while his good friend is doing the most ludicrous thing possible is the best way to honor him. It would almost be insulting to do it in a reserved or serious way. that just wasn't him. And the pixie dust thing... eh. Roner obviously didn't mean it in any disrespect. I don't see a problem.
Although I'm kind of curious on how he was given Shane's ashes as opposed to the family. I guess they figured roner would be able to do it the best way.