I assume your referring to one thats for sale right now.
I'm not sure I personally place much of a premium on it above what a normal machine is worth.
Maybe there are people that do, but I'm not one of them.
The problem is that the machine is already so much money, how much can it actually ad to the value.
Don't get me wrong, its interesting as hell and its a neat part of the games history.
But frankly from what I can tell, its just subtle changes in the play field (wording and such).
I have a CV, and wouldn't care either way if it was an early "sample" or not.
It does make a more interesting conversation piece though.