There is not enough difference in sound quality between on-board vs dedicated sound for the typical user, making a question of "sound quality" incredibly subjective and a poor basis for making an $80 gamble.
Just because the typical user (possibly yourself included) can't tell the difference between on board audio and a dedicated sound card doesn't render the exercise null, let alone a gamble.
What we SHOULD be looking for is a sound card that IMPROVES THE PERFORMANCE of our PC's... a FAR less subjective metric.
Actually a far more POINTLESS subjective comparison considering how little it affects modern CPUs, with or without my sound card I notice zero difference in CPU usage. You go on to say this yourself in the next paragraph even...
On-board audio actually uses a *tiny* bit of CPU power that has a tiny impact on performance depending on the bitrate, number of channels, and complexity of sounds produced. Arguably, a sound card could be produced that IMPROVES cpu performance while allowing you to tax the audio capabilities of your PC.
Unfortunately the task or reproducing acceptable audio had long been the task of on board solution which have very little impact on CPU usage in most scenarios. By having a dedicated sound card your taking so little away from the CPU that performance gains are so negligible you can't use that as an argument anymore. If you have a suggestion on how a sound card can "IMPROVE" CPU performance I'm all ears, the second half of your sentence stops making sense however "while allowing you to tax the audio capabilities of your PC" please elaborate what you mean by this.
"Sound quality" is too subjective. We need to ask a different question.
Anything related to a human sense perception is going to be "subjective" bases on the individual, we all hear things a little differently and are willing to make different sacrifices when it comes to audio quality. For example I refuse to listen to music through the built in speaker on my phone because the sound reproduction is too crap and bothers me, others seem perfectly fine with it, thus the subjective nature of audio.
After using a dedicated sound card for the better part of the last decade I'm a strong supporter of the idea, but also feel it something that won't necessarily benefit everyone, the best example will of course have to do with cars. Not everyone changes their factory head unit/speakers/adds an amplifier, even less so these days with the entertainment system coming from the factory that boast relatively good specs (Much like modern motherboards). But I wanted more, the same way I wanted more in my PC, so I changed my head-unit, all my speakers, added a subwoofer, dedicated amplifier. None of this would be terribly important to the "typical user" but for me, and many enthusiast like me, we do see a reason, and also understand it's not for everyone.
So instead of asking a different question, understand the reason to the question being asked.