Capped off?

If the caps have a pin then they are shorting-plugs and should only be used on RCA inputs. Not all components can use these.
Regular caps can be used anywhere.

+1 tube_gb

I use them as well....more to repel dust than for any sonic benefit. I really have no idea if they have any effect on sound quality.....but as you say, they do look good.

Shorting plugs are what is used for crosstalk. The plugs that you have are dust caps! This is what a shorting plug looks like!
https://www.amazon.com/Viborg-Stopper-Plated-Copper-Protector/dp/B017DH76VS/ref=sr_1_3?dchild=1&...

Just get the cheap ones with removable pins. Go whichever way works the best. 
If you gotta spend up, FutureShop UK is your best bet.

I don't know about Cardas, but if you were using the old PPT caps there would be no doubt. The reduction in noise, improvement in clarity, and image focus, is obvious and easy to hear. 

That's the problem with these things. Tweaks, I mean. Someone makes one that is truly outstanding. Everyone hears and says wow that is amazing. But then instead of buying the good stuff they decide to try something else. Which of course turns out to be crap. Or they use something that looks the same, and jump to the conclusion it is the same, and then in a Beamon size leap of logic conclude everything that looks like that is snake oil, to use this sites preferred vernacular.

Get the PPT ones. If you can. Anything else, oh well.