To me it sounds like you experienced a nickle-dimer low-baller. Most of the issues listed are inexpensive fixes. Is this a T-Top T/A? Even if it isn't, and if the paint is good (no mention of it needing a paint job) you should at least be $9K-$10K for a 59K original mile car. Very nice 79's are listed for 12K-$27K on eBay. I sold a 79 T/A project coupe, 403 that needed rebuilt, had a seriously rusted-out quarter panel, floor board rust, very sad and incomplete interior, oxidized non-factory paint on eBay for a respectable amount. There is no way I would have let yours go for $5K.
Hope this helps. You may want to sell on eBay - eBay has great market coverage.