They see it as a way to show that they're better fans, because they're able to feel happy for him. It's less about Jensen, and more about improving their status in the fandom.

I think you definitely have a point here. Also, especially since some of the BNFs are vocal about their excitements, other fans are likely to be jumping on the bandwagon.

I can see why people become so involved in the lives of celebrities, but personally, I agree with you: they're not people that I know personally and thus are no concern of mine.

All fandoms have their crazies. ;) A fandom wouldn't be a "real" fandom without wank and rage and people taking offence left and right.