The thread seems to have derailed somewhat into a discussion on the best forms of processing, so here's an attempt to re-rail it and answer OP's question.
The reasons why I think people still like old boxes:
1) A bit of nostalgia - 'radio how it used to be' as mentioned above. Takes one back to the days when radio really was a lot more fun.
2) They look cool. You have to admit, the 8100A is a great looking unit. Intuitive, informative, commanding.
3) Real knobs to adjust and meters to look at. A control room just isn't the same without lights, meters, knobs and dials. It's hands-on.
4) Comparatively cheap - compared to a new digital box which can be upwards of $10k.
5) Easy to get that 80s analog sound. Plug in, turn on, adjust levels, done.
6) Vintage = retro/old school = big money. People like old stuff, if it can still be used today. It has a certain appeal to it.
7) If you don't like digital, they are a good box of choice.
It seems that radio has become more IT than 'radio' over the years. I love the sound of the Breakaway system, but I am torn - the 8100A Optimod box just has that 'radio' look about it. The LCD screen and lack of knobs and meters on a digital box just isn't the same.
A rack full of computers just doesn't compare to a rack full of analog processing.
I see a challenge for someone - design a retro-fit Breakaway system to go into an 8100A box, that still keeps all the meters and LEDs operational. Now that would be one VERY cool piece of equipment.
Can it be done? I am sure it could. The same basic principles apply - L and R audio in, composite out. You've got 8 or 9 slots to play with, you could spread various parts of the system across different boards. As far as a display goes, you could mount it behind the door.
I agree it's a little incredible that old technology commands such high prices. There has been a bit of hysteria over 8100 Optimods over the years. They were once one of the most expensive processors on the market. (Does anyone know how much a brand new 8100A was when they were in current production?)
People's perception of what something is worth can be influenced on the social 'buzz' which surrounds it. If word spreads that a certain item is really good and has great value, people soon believe it and the price goes up accordingly.
There might even be some sentimental attachment to these old boxes. For those of us who installed them new, who worked with them and don't like to see them end up in a dumpster.
Ok, that's my 2c worth.