I did Seattle to Frankfurt direct with Lufthansa in December of 2008. While not AF, they both fly Airbus and are both direct. If the difference is less than a couple hundred dollars a ticket, it is probably worth it (for a couple of people). I have a policy against flying through domestic airports to save money- my brother and wife had a travel nightmare going through Chicago from Seattle on "cheap tickets" to Europe.
I have now been researching open-jaw Seattle to Paris and then Frankfurt to Seattle flights. I found Lufthansa to be fairly expensive to add Paris on to the route. British Air is the cheapest for when I am going (December), so far, but I am not sure how I feel about Heathrow. (We wouldn't mind checking out Harrods or Gordon Ramsay's restaurant, though!)
However, my parents just took Icelandair to Frankfurt, and I recommend taking a look at them. Customs in Iceland is supposed to be the quickest in the Schengen countries (you would not need to repeat customs in Paris), and with a smaller 757 they can go through a whole flight pretty fast. My parents' lay-over was just about 45 minutes, and it broke up the flights and gave them a chance to stretch their legs out. The total flight time + lay-over time was not much longer than a direct flight would have been, because they were not back-tracking. They were very happy with their experience.
If the savings on Icelandair is substantial over Air France, it is worth taking a look at. Over all the 1-stop flights, my research (and parents' experience, not mine), shows Icelandair to be a good deal.