I agree with those who say donate it. First look around and see if anyone in your circle of family and friends could use it, including young people. Then look at charity sewing groups - senior centers, church groups, guild work groups, etc. Having some of the decorative stitch functions inoperable is not an issue for them. If you do have any feet or attachments that are out of the ordinary, you could definitely sell them on Ebay or elsewhere.
If it stitches, it is worth something to someone, and there are people who would be grateful to have it!