Well, it definitely helps, especially with the age of these caps. Use high quality caps like Elna Silmic series for the best results.

Although I've replaced the capacitors on three Sound Blaster 16 cards I actually care about, I'm fairly certain only one card actually needed it. I bought it cheap because one of the large capacitors had been torn off. It worked as-is because the missing capacitor was part of the amplifier circuit which I never use as I use active speakers from the line-out jack instead.
I replaced all the caps while I was at it and immediately noticed that the sound was far clearer and less muddled if you get what I mean. Especially the low end.
Anyway, it was still incredibly noisy until I swapped the newer DAC from a dead card so if you're hoping it will clear up the high noise floor/(what sounds like) tape hiss, I doubt replacing the capacitors will have much effect.
The other two cards I just did preemptively as they are both ~30 years old. There was zero audible difference to me but I'm still glad I did it.

Just re-reading your original post and I forgot to mention the fact that I have a CT4520 in a Pentium II system. It's incredibly quiet. I haven't changed the capacitors on this yet but the DAC is not going to be a problem on this card. It's too new and Creative seemed to have figured it out by then. I'd try replacing the capacitors. It's a cheap thing to try if you're comfortable with that sort of work and as stated before, the ones on there are fairly old. They also didn't really use the best ones to begin with most of the time from what I've seen.

The capacitor replacement did help bring the noise floor down (so far just done about 80% of them, didnt have some values in stock).

I've gotten drunk and haphazardly replaced all capacitors on my PCI ESS card once. It had better mids but much worse noise and his.

Derp.