I think the most impact this online community makes is not actually to Broadway shows, but rather off-Broadway.
There are only 40 Broadway theatres. There are HUNDREDS of off- and off-off-Broadway productions. It's impossible for one person to see them all.
When I read on BWW that there is a lot of positive reaction to an off-Broadway production, I'm much more likely to go buy a ticket to that show. In fact, sometimes that show may not have even been on my radar!
The best example of this, for me, is SLEEP NO MORE. I would have never, NEVER thought once about actually going to see it...until all of the positive response here on BWW.
"The Spectacle has, indeed, an emotional attraction of its own, but, of all the parts, it is the least artistic, and connected least with the art of poetry. For the power of Tragedy, we may be sure, is felt even apart from representation and actors. Besides, the production of spectacular effects depends more on the art of the stage machinist than on that of the poet."
--Aristotle