Depends on what you plan to listen to. If you have reasonable speakers, play games and want 5.1 or higher quality music, then an Audigy2 (around $60 for the non ZS one) would be a very noticeable upgrade. If you have $5 speakers and use your PC for Excel, its probably not worth it
I recently went from a SB Live Value! with Logitech Z 560's, to NVidia Soundstorm with Logitech Z 560's and wow what a difference that made. With the Live Value, music always sounded high strung and very bland, but with the Soundstorm, it sounded a lot fuller. more mids and lows, and a generally more rounded sound. Not mushy mind you.