If you're just listening to music or playing games, stay with the onboard - especially if you don't run your rig through a professional sound system.
As apposed to what? Isn't that what most people do with their PC's? Play games and listen to music? I've compared my Logitech speakers to so-called "home entertainment" systems, and the sound quality of the Logitech’s was just beyond words (PC 5.1 surround speakers vs. 5.1 home entertainment system - for half the price, R700 vs. R1500). I have an extra set of 2.1 Logitech speakers that I hooked up to my TV, and it STILL sounds better than other home entertainment systems. (and I'm mostly referring to systems that are within affordable reach of most people).
It is a debated point that sound cards in SA are overpriced when compared to abroad, but so is most other PC components. I also had (still have) onboard sound, but I got myself a proper sound card because I wanted to improve my listening pleasure (for games, but mostly for music), just as one would buy a faster CPU or bigger RAM for better PC performance. Stating that, soundcards are still a "luxury" item, as apposed to things like CPU's and RAM, as it is not a crucial PC component. But then why would you go and buy a 19" LCD monitor over a 19" CRT monitor? Because you can.
Besides, I've found that there is things add-on sound card's software allows you to do that most onboard sound card's software probably just wont. For example (and this is not the only thing that's good about it), with the pci sound card I've got, I can tweak the 3-D effect of the audio output, something I couldn't do with my onboard sound (and believe me, I've tried). When you've got a 5.1 surround sound system, this makes, in my opinion, a HUGE difference, with games and with music, 'cause usually it appears that no sound would be coming from the rear speakers, even though there would be (when using onboard sound). However, I never had the opportunity to test other onboard sound cards, and I understand that the more recent motherboards are bringing out better quality onboard sound cards. And following the sound upgrade, I've never regretted getting it.
So sure, if the guy is using plain, crappy old desktop speakers, than there is no point really in upgrading the soundcard. But I'm assuming that he wouldn't have posted the question if he didn't have at least a reasonably good speaker setup. And agreeably, the Audigy 2 cards are a lot cheaper than the current X-Fi cards, and probably do exactly the same job. So if you've got the money to spend, upgrade the sound card, if you feel sound is important to you.