The Zbrush forum here on renderosity tends to be a little dead so you may want to try Zbrushcentral.com. But to answer your question YES. Zbrush is way worth the 550 or so that they are charging. Plus you will be able to use along side of max but after using it a while and getting used to the interface you probably wont even want to model your organics in max anymore because of the speed and power of Zbrush. Also if you are in any kind of gaming field the ability to extract normal maps from 1million+ poly models for your few hundred poly models and have them look almost exactly the same is priceless. The same with displacement maps but you get a lot better result but i dont think that any game engines support displacement mapping yet. Pixologic has a free demo if you want to check it out.