Points in my post above aside, I feel that specifically for O Gauge trains, the semi demise of MTH played a large factor in some of these insane prices. It would seem that the new Lionel catalogue's prices may not have spiked so dramatically if it were not for a significant reduction in the competition.
Look at what they are getting for MTH subway sets (used ones) now that no one is making them. A year ago or so new ones were greatly discounted below list. Now used ones are way above list.
John