yes indeed it is a matter of personal opinion as to the value of an n800 to an n810 or n900...
I have and do use all 3.
Have for years.
And I know that when it comes right down to it...
sure I use my n900s..they are great...
But they don't have a place in my heart like the n8x0's.
Anyone who has spent time with the n8x0 line knows what I mean..
and that feeling doesn't wane with the passage of years...

As far as a professional opinion goes..
if one were to put value on the nxx0s as to what they are worth...
well..
When the last n900 breaks down..sad day it will be...and that day will come when there are none left functioning...
Sooner than many think too...
But..
the n8x0s will still be running...and running and running...
their build quality is superb ...with virtually no physical fault built in.
And I expect there will be a possible resurgence in use and devel and maintenance .. in the n8x0 line then..
There is most certainly value in the "last devices standing" .