If you are selling stuff, such as fruits, vegetables and fish, to the supermarket instead of just through your inventory, I remember reading somewhere that you get 10% more for it than just selling it in the inventory (haven't confirmed it myself, but if anyone wants to, be my guest). Thus, I think this is actually a valid question. There would obviously be a reason why the developers included the possibility of travelling to France and sell it, so it would be illogical to dismiss that possibility before someone has actually tested it.
You absolutely get a better price on the fruits vegetables and fish by selling them at the store - I've confirmed that. I also got a 10% premium at the Nectary for selling wine I made myself there, but no bonus for selling wine I found in the game at the Nectary over selling it in my inventory. At about 1.5K simoleons base price per bottle when I'm ready to sell it and a cellar full of racks of aging nectar, that 10% premium really adds up.
I agree, I wouldn't make a trip just to sell wine because it's a pain in the butt, but now that I've got a comfortable vacation house there and a certificate of partnership, the premium on selling the wine at the Nectary pretty much pays for the trip for my whole family (and then there's the payoff for opportunities while there, all the titanium to pick up, all the books I can write off the aging clock...) my last trip I bought land, built a house, bought a car, and made about 20K simoleons on the trip.
