EMs are good nostalgic pieces but I'm glad I got the last one out of the house a few months ago and it was from the mid 70s (sold it to a neighbor who wanted nostalgia).
I have a nice 60s Wlms 8Ball in the garage - 3 reels with a light for the "thousands" but it will soon become a coffee table (or I'll junk it out for parts and to make room).
The evolution of popularity and value is interesting. In the 70s the old "wood rail" pins from the 50s were considered sought after "classics" but the interest and value has greatly decreased. There are a few of the early 80s solid state games that seem to have retained some popularity and value - the Bally EBD and Fathom are examples of the few.
I agree re craigslist -I bought the 8Ball for I think $40 from a CL seller and I see games from the 60s and early 70s regularly.
Our last EM was a Bally "Old Chicago" in great shape, it had nostalgic history for us and it was and is one of the faster and more challenging EMs BUT when you only have space for a few games the "keepers" are the mid 90s Wlms/Bally - even Gottlieb/Premier - to us.
Good Luck finding the 60s machine you want.