I think the only thing worth pointing out is that shitty caps will degrade over time faster, causing your audio to degrade or die also. On Pci sound cards though, those cards do not run at high temps, and are usually placed in a place with decent space or air flow, so the caps on them last a pretty long time as they are normally already rated for 85c or 105c and have low esr, like the Luxon and Rubycon low esr caps, Sanyo OS-CONS, and most normal decent SMD caps, etc. Higher end sound cards released today with high quality Japanese solid caps, even more so. Back in the ISA days, sound cards really did have noticeable varying sound qualities when you compared cards though. This was due to a number of factors, not just limited to the types of caps used, but also due to how components on the cards were laid out. A good example would be the AWE32. It had a messy layout and was pretty noisy. The AWE64 corrected much of that problem by streamlining everything.
All of this is almost moot for the average guy just running a $50-200 dollar speaker set up who cant tell the difference in sound quality from a Hercules Muse XL, Turtle Beach Montego, and a SB Live! Value. About the only way your going to notice any kind of sound quality difference really is with some good sound measuring/monitoring equipment spitting out data for you to view, or a really high end sound system in a room with padded walls and great acoustics. Otherwise, all this amounts to maybe is a really picky person hearing noise or clarity that isn't really there.