I am no expert but I would think that machine options determine value at the end of the day (a side note to recognize condition). If you have 2 80's machines of approximately the same level of wear/use the one with the best features should be more valuable. e.g. if it has multi-ball or not (or theme if it's popular). Also have to consider the nostalgia factor.
As people get older I really don't see much of a market for woodrails for an example. As there's less people around who hold the nostalgia factor (that are willing to shell out for a machine) the only reason to buy up one would be a great theme/art or in the hopes that it will provide profit when sold down the road at a later time.
Still, if I had to choose a woodrail or a machine with ramps or multi-ball (for the same cost) I am going to get the machine that provides the most excitement for my dollar.
That being said I may consider a Spin Out just because it fits my current auto theme my collection currently has (if i can get one cheap as I am not overly fond of EM repair).

At the end of the day I have to consider it a hobby and not my 401K