The Cinemaquest/Audioquest plugs in the OPs pic are
silver plated not gold, so they are simply tarnished. One of the reasons nobody uses silver... Even if you clean them, they will tarnish again.
I prefer this style because you can just insert a pencil into the tip and make them as wide or narrow as needed, so they always fit tight. They have a slight spring action and compress as you insert them, so they tend to stay tight all the time. They can be a bit more fragile though, don't really lend themselves to a lot of lateral pulling. I had one set of speakers with an odd size binding post and these were the only ones that would stay.
On my amp side, I use locking ones: