I am not really qualified to say much about Imperial knives but I have owned several.
Some of the guys here collect them so I guess they are collectable. I have never been impressed with the quality at all. I am not sure about the steel but the ones I have had have not been bad to rust. I have never considered them a knife I would use on a day to day basis if I had much work to do.
Most of them I have had had metal handles some covered with some vinyl material. I myself prefer to concentrate on fewer knives of better quality.
To me it would be a very rare Imperial that would fetch 50.00 on Ebay.