I have a VIA VT2012 or something along that line (can't quite remember) which seems really similar to the ALC1150 and I switched out to a Sound Blaster Z, but I really didn't notice much of a difference at all between the actual sound quality. I'm using it with Beyerdynamic DT660's and Logitech Z-2300 speakers. So, although my gear is hardly top end equipment I wouldn't call it entry level stuff either.
The SB Z does have some neat features like being able to save profiles for each output device (though I haven't found a way to auto-switch between them) and the nice feature of being able to plug both your headphones and speakers in at the same time and swap between them via software (which is still kind of annoying because I haven't found a way to macro it or automate it), but I wouldn't really call that worth the hundred bucks you pay for it.
So, unless you have some serious problem with your on board (like static interference, unable to drive your headphones properly, or some other problem) or you need some feature that the cards have I'm not so sure a dedicated sound device is all that required if you have a fairly decent on board audio solution already available.