If Aston Martin decides that they want to sell the James Bond car to the public they should be able to. It is up to them to decide if and when to sell it and who they want to sell it to. It is no different than any other car.
I think the price tag will limit the market, but if the market is there and buyers can afford to and want to buy the car, then they should sell it. If someone really wants the car, they will find a way to buy it. For most people, it will be only something they can see in the movies, but the insurance alone would be out of the price for most people.
It might make the James Bond franchise even less cool than it has already become, it might only sell to rich dorks with no taste, but, as a huge, evil corporation, Aston Martin can, and should, do whatever they want, even if that includes destroying the magic of decades worth of adventure and action movies.
No, I don't think that Aston Martin should sell the specially made James Bond car to the public. Yes she could get millions of dollars for it, but they are already rich so they miswell keep the object that is worth the money instead of take the money that they already have.