A GoodShows type site would be tough. I'm also a theatre reviewer, and have seen the same show done many times by different groups. Several times after the first viewing I've thought "I never want to see that again." Then it turns out I have to see it again some point later at a different company, and it is wonderful. And the reverse has happened, loved a show the first time, seeing it later, hated it.
If people think something like this would actually be useful, it would be somewhat trivial to get something up and running. Either a forum system, or a wiki. I'm willing to start a sub-site under my theatre review site.
