It was my understanding that this was a "lawnmower" forum that was here to deal with mowers that get pushed or at least...you walk behind. So I'm a bit surprised to find discussion about garden tractors here. Call me crazy but I thought that those discussions belonged on MTF.
Anyway, I'll clarify a few things here.
First off Case and Ingersoll are NOT the same company. Originally, these tractors were made by the Colt Manufacturing company and J. I. Case bought that company in 1964. Then Case SOLD the company to John (Jack) Ingersoll in 1983 who then sold it to the Rothenberger Group out of Germany who later on place the company into Chapter 11. Eastman Industries then picked up the company, moved it to Maine and is producing product today.
There is no connection to Gravely, Allis Chalmers or Simplicity that I've been made aware of.
I'm not going to bother getting into values because this is an old thread and the OP has not shown any further interest in it.