Were this my bike to sell, I would clean everything GENTLY, so as to leave patina, but to remove dust, dirt and grease AND to allow for a really good inspection for any damage of any sort. I would clean all bearing surfaces. Not so sure I'd relace the wheels, though. In this case, what you really have is a project for a collector of what is frankly a niche bike. You need a Francophile to buy it, because this one is as much an artifact as it is a bike, and it both suffers from being BEFORE the models that have the greatest nostalgic appeal in the U.S. (Super Corsa, TdF, even the Interclub) while benefiting from being a pre-bike boom machine that the serious cognoscenti might adore. Where's the Jacques Anquetil-wannabe when you need him?

I would research 1969-71 Gitane Professional Super Corsas and price comparably. If you researched comparable condition Tour de France model from the same year, that would be your floor I think. This isn't an exact match of the '66 catalog, but Gitane built different bikes for different markets.

EDIT: Go here and look at the entry form the 1966 price list for the Gitane Professional. There you are!