Thanks again this was for my son, but has turned into quite a hobbie for me this winter as well.
I would imagine that it isn't doing too much harm letting them sit. The only thing I can think of is the lube that is in them might get "junky" and thick, other than that I think it's ok. Those old Lionels are all metal and built pretty tough from what I remember. I still have the one from when I was little and it still runs fine, just have to lube it up a little when I run it occasionally.
Yea, I think they would be ok as well. For Christmas I got my son one new train set and one very old (but still in the box) train set. When we took the old one out to test it, it just buzzed and wouldn't run. After cleaning and oiling it up it runs great. So just a good cleaning and oiling is all they should need.
Now that it is set up, I just need to cover it up and get back to polishing trim.
Dave