We didn't get to see very much in utilidors...just lots of lockers and lots of concrete...we saw a costume area further down the tunnel, but it was so far away all we saw was a half dressed Eeyore.
If you are taking the tour to see the tunnels, it's not really worth it. The tunnels are just dirty cement walkways...we thought there would be more to see. They take you upstairs to an office lobby behind main street where you can see a couple early pictures and some displays on appropriate CM apparel. We also got to see parade storage and ride parts being repainted.
We did the tour Dec 04, but you may get lucky and get to see more than we did. We got 2.5hrs of disney history and 1.5 hours of rides and backlot tours.