Live sand in a bag really isn't important. It's the same thing as using live bacteria in a bottle. It provides you with nitrifying bacteria, but it is not "live" in any other sense, and honestly, the little packet of nitrifying bacteria that is provided with the "live" sand just goes into the water column anyway. I wouldn't waste my money on "live" sand.
The other benefit I see from using "live" sand is that the tank water clears faster, but that's simply because the sand has been wet for a long period of time. If you pre-wash new, dry sand and then let it soak you'll achieve the same thing. You can even wash the new sand with "used" saltwater from each water change if you really want to.