Hugh, you've hit the nail on the head there. People don't like unknowns, and I have two cars that are in a similar plight. It will take some work to make them presentable, but doing so will almost certainly quintuple their value. What's a day or two of work to get that sort of return?
I do suggest that if the paint is intact that you hire a detailer (assuming that you don't have a buffer and the skills to deploy it). Getting the paint all shiny and clean can make a silk purse out of a sow's ear in no time.
I have normally recouped the $100 spent on detailing several times over each time that I've done it, plus it makes the car look fantastic.
Good luck. I look forward to a picture of your smiling mug sticking out of the DS window on the 1973 page. Who knows, maybe it won't go back on the market! Imperial Margarine certainly worked its charms on me.