It's a great experience...do it. Ask for a vintage cabin so you get the full experience. A lot of history there and the tours are very interesting.
We were lucky to stay once during a meeting of the 'art deco' society so everyone was dressed in period clothing. Having a cocktail in the bar was fantastic especially with most guests in period clothes.
On another occasion there was a huge wedding party and that was not as good. The walls are paper thin as they were when it sailed. It was a bit loud.
We have a very detailed book on the history of the QM, that would help you enjoy her even more.