I went and saw a pantomime in Bath when I was in the UK. Indeed, I managed to persuade my mother to arrange the trip to Bath around the panto dates so I could see it. The reason? Colin Baker (whom I wouldn't call a has-been) was in the show. It was Jack and the Beanstalk, and Colin Baker was the villain, Fleshcreep.
It was...quite the experience. Seriously. Besides being strangely highly entertaining, you will never hear anything like Colin Baker singing Let's Do The Time Warp Again from The Rocky Horror Picture Show. He didn't quite hit all the notes, but he more than made up for it with that damned powerful, operatic (yes, operatic) singing voice.
The Doctor: There's one thing you never put in a trap, if you're smart, if you value your continued existence, if you have any plans about seeing tomorrow, there's one thing you never, ever put in a trap... Me.
-Doctor Who: The Time of Angels