In 2006, my DD-8 also got to help pilot the Mark Twain. She thought that was soooo cool!
We have only ridden the Columbia once because it seems to always be down when we are there. It was a pleasant surprise to find that they had a sort of museum down below.
Both are really beautiful because of all the detail they have put into them.
We have piloted the Twain in the wheel house twice. Very nice experiences, both times.
A first for me last week though was watching the fireworks from the top deck of the Twain. Since Fantastmic isn't running, they are running the Twain at night. It was a neat perspective and you could actually see Tink fly really well.
On our 2006 trip my girls asked the captain if they could steer the Mark Twain, that's a great memory for us. We never get on the Columbia, it's not out enough.