Come for the conference, stay for Paris. Seriously, if you've never been to Paris you really should do yourself a favor and hang out before or after the conference. It's an amazing city and October is a really great time to be there.
Yes it is! We will also do a RailsGirls event on the weekend after the event. And we will be happy to help anyone organize a longer stay in our city ;-)
If you do go to Paris, make sure you check out the catacombs: http://en.wikipedia.org/wiki/Catacombs_of_Paris - they're not at the top of most people's lists but they're spectacular and unlike anything you'll see in any other city.