I'd say save up for a new MB/RAM, not just the RAM. The Audigy and the Live are *identical* cards with the exception of the Audigy having a Firewire port. They use the same chip and everything, and no audio advances have been made on the board, maybe a better process for a slightly clearer sound, but you won't see a night and day difference (or even day and dusk). 256 MB more of RAM won't give you any better performance than you already have. Your video card is near top-of-the-line, and your CPU is plenty good. If you picked up something like the ECS K7S5A, you could use your current CPU and RAM, and then move to DDR when you're so inclined, but be forewarned, with that board it's either hit or miss. My roommate has one and it works perfectly, but I've heard plenty of horror stories, as well. I think it's about on the level of horror stories that people tell about any board, but it's just that more people picked up that one particular board in general, so more people reported problems.
Anyway, take a look at some MB options if you're so inclined, but for your particular question, I'd say neither are recommended upgrades. If you're desparate to switch sound cards, I picked up a Turtle Beach Santa Cruz after my SB Live Value and I can tell a differenc ein sound quality in favor of the SC.