Eric, I see your point, although I don't think comparing cars with these machines is fair.
Cars are always changing with the times, but they always remain that...... cars. 4 wheels, windows, steering wheel, bumpers etc...
So there are always "collectors" of cars, of every era. With people getting older, they gravitate to what they remember as a kid, or what looks good to them.
The prices of the 30 and 40 and 50's cars might have dropped over the years, as the muscle cars have taken their place, and or the $$ that people have to spend on a "toy"
In saying all that, there really is not anything that will replace the RT machines (other than a couple of squares from the early 70's) The machines of today are just BIG boxes that have no style, shape, or appeal to be a collector item. The machines of the 80's and 90's are so massed produced, large, plastic fronts etc. I just can't see them to be a collectors item either.
So, if these machines do drop in value over time, it's only because people in the future have no interest in them. Their "collector" dollars might go towards something else. Where as the car money of the 40 and 50's are going to the cars of the late 60's and 70's.
As long as there is Coca Cola, and the branding, marketing, etc that goes with it, I think there will always be a "want" for these machines, but in terms of value, well, it's what the market will pay.
Juke boxes (from what I've read) have not held their values over the years, but again, it's because tech. has changed, where getting a record is tough alone on it's own, never mind the fact that kids of today and tomorrow listen to music in digital forms.
If Pop were to stop all production of glass bottles, whcih might very well happen one day, then that could hurt this hobby. But the machines themselves are a pop culture item on their own, so the babies of today who grow up to be stock brokers, will want to look cool in their condos in the year 2050, and will want our RT machines lol.
It's tough to put a 1959 Cadilac in the garages of today that are made for a KIA, not to mention puttin a 59 Caddy in the man cave.
I have to do some work now, so I better stop.... and yes this topic has been brought up before, but I like how new people, even myself, still think about this topic, and it keeps the hobby going.