Waves Center?

Center is cool, but you can do most of what it does with Channel Tools. 
 
What CT doesn't have is separate EQ and other processing for mid and side.  But you could accomplish that by duplicating a track and inserting CT on each, one for Mid and one for Side, then tweaking and going far beyond what Center could do by itself.  So Center could save time, depending on what was needed.
 
Other plugins like the brainworx stuff, MeldaProductions, and Ozone also do M/S processing, so check your toolbox to see if you already have a Center equivalent.  But if you do decide to buy it -- presumably after you've demoed it -- check sites like PluginDiscounts, where they're selling it for $40.
 
Cheers,
Eddie