I sold a Pfaff in a cabinet similar to yours, a couple of years ago for $78.00. The Pfaff is considered collectable. The "15 clone" machine category, which your machine fits into, are usually great machines for sewing and yours appears to be in great condition. You can usually get parts if you need them, as there are lots of them out there.
There aren't a lot of collectors for them, however. If people do collect, it's usually the colored ones, not the black ones. Enjoy it and don't worry about the value. If you're trying to sell it, put a "reasonably" high price on it and know that you will probably have to come down on the price.
bkay