There is no difference at all between the Soundblaster Live! Series. X-Gamer, MP3, Platinum and Value are all the same cards. They just come with different sets of software. Games with the X-Gamer, sound editing stuff with the MP3, all of it with the Platinum plus the LiveDrive, and just the basic LiveWare with the Value.
Now, when you compare any of the Live cards to say the Ensoniq, or Soundblaster 128, there is a world of difference. The Live cards output true 5.1 (older versions 4.1) surround sound. They also have EA, environmental audio, supported in a good number of games, such as Rainbow Six: Rogue Spear, Deus Ex, Unreal Tournament, etc. EA just makes things sound incredible. You get much clearer sound with the Live cards, which may be indistinguishable if you don't have good speakers. The Live cards handle mulitple wave outputs, use hardware acceleration of coding and decoding (mp3 audio streams, avi's and other movies), which ease the load on your computer's processor.
All in all, the Live cards are worth it. But, go with the Live Value, which is really a great value for under $50, and the same card as any of the other.