Don't know about the MTH stuff, but for the original prewar, your $ values are probably ok. The trouble will be actually selling it. There is just an abundance of junk/parts items at meets. I struggle giving some of it away even with 2-3 cars for the price of one at $10-15 sometimes. The customers for this stuff are typically people needing original parts, or restorers.
Thanks for your input. I'm more comfortable with my knowledge regarding the MTH items, so you filled in the blanks on the O gauge.