Rarer than a Mustang. Rarer still with a manual transmission (3-speed or 4?). But sadly it will never be worth as much as a Mustang since rarity is not the sole driver of prices.
If it is a solid as you say, I wouldn't chop it up. I'm in the same boat as you except with a 67 Olds Vista Cruiser I bought as a parts car (and paid way too much now that the market has tanked). I don't have the resources to fix it up right now so I'll probably sell it and take a loss on it. I could make more by parting it out, but I hate to do that.
depending on options, color ect... is how much it is worth. They are not as popular as mustangs but they have a following. if the body is in good shape i wouldn't cut it up. There are plenty of rough-er ones out there that could be cut up and fixed up they way you want.