I had no feelings one way or the other for Princess Di while she was alive. But I do have to disagree with your description of 'near mass hysteria'upon her death.
It was immensely moving for some people for all sorts of reasons...

1. The shock of a celeb unexpectedly dying.
2. The loss suffered by her family and the kids were young at the time.
3. The tardiness of the Firm to issue a statement, bearing in mind their attitude towards her prior to her death.
4. The realisation that she had actually been a figurehead for numerous charities, and they would have a knock on effect by her departure.

and so on and so forth. The out pouring of grief was always going to be as large as her presence had been in public life. That IS perspective.

As for Ken Bigley being mourned by people who didnt know him...if it gave his family any comfort at all, then why is it wrong?