Sure, it's worth it, if this is a direction that interests you. There are a ton of different approaches, though, and you should decide what sort of thing you're trying to do, and what program or system would be best for accomplishing that. If you're into the hard-edged geometric type of sculpture, Z-brush probably isn't for you - a program like MOI, Rhino, or Solidworks might suit you better. But if you're more interested in organic, textural sorts of things, then Z-brush, Mudbox, Modo, or Sensable's Claytools would be more appropriate. Any program you get into will take some time and practice to get good at, but it might save you some time and money over making your mistakes on a grand scale with real materials like stone and bronze.
Obviously, if you're looking at sculpture as a recreation, something therapeutic to do with your hands after a busy day at the computer, then this probably isn't the approach that's going to appeal to you. But if you want to be able to test out 3d ideas without wasting valuable materials, then it has a lot to recommend it.