Depends on a number of things.
If you like keyboard instruments, and it works, you should get it.
If it has a big old Leslie speaker cabinet you should get it. These are all worth more than $40, and seem to be easy to sell.
If its a top-of-the-line Hammond, regardless of age, it is worth much more than $40 as a unit or in parts.
If you can absolutely confirm it is a tube unit you should get it. These are all worth $40 in their amp alone, and many can be parted out to supply expensive older tube Hammonds. There are at least a few ebayers doing this on a regular basis.
Otherwise it is a crap shoot. Organs are heavy and aren't always easy to sell. Many newer Hammonds used fairly cheap internal speakers, and most of their entry level solid state amps aren't all that special. If the unit isn't working right, you could easily spend far more in repairs than the unit is worth.