I recently upgraded from a Realtek 8 Channels ALC888 integrated Audio controller to the Audigy SE.
(Like you I was wondering if it was worth the money)
Result :
A slight increase in sound quality. Also I like the Creative Audio settings. it's a bit like my Iriver MP3 Player "3D" mode, although the Iriver still deliver the best sound quality of any hardware I have owned.
I also got a tremendous increase in Microphone input quality.
It's was one of the reason pushing the upgrade. I got crappy result with the Realtek microphone, and the micro integrated to my Microsoft webcam was not that great either. I was used to power on the Thinkpad for skype calls as it got a very decent micro.
Now recording quality is great, even better than on the Thinkpad.
If u want better quality you have to pocket much more money for the next good offering.
I understand that the first cards in the X-fi line (xtreme audio and xtreme player) are almost the same hardware wise as the audigy SE, with an heavier software package, so It don't seem a good deal. So if you want better you should look at the mid range X-Fi.
You may also want to read the user's reviews on Newegg, that here that I found the more user's opinions on the Audigy and on the others cards.