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.
"What have you been doing since you stole that antique TARDIS of yours, since you first landed on Skaro? Shouting 'Look at me!!! I'm not fighting a war!', while you battle the Daleks all the way through space and time."