I'd love to do the Vasari corridor tour with my kids ages 6 adn 9 -- can anyone tell me if the tour would be good for these ages, or too long and detailed?

Here are two articles from the Slow Trav site that describe the Vasari Corridor tour. A review of them might help you decide if the tour would be okay with your kids.

Walking in the Footsteps of the Duke

Vasari Corridor - Paradise Gained

I would say that it isn't a very good tour for kids and might distract other people. Palazzo Vecchio has a far better special tour for children. If you go to the ticket window you can find when it will be. They take you through secret passage ways and the children get to meet "Duchess Eleanor of Toledo." This was my blog entry and pictures the day we took our 8 year old Childrens Tour You will enjoy it right along with your children.