There's no problem with having gold-plated binding posts on amps and speakers. Pretty much all posts are gold-plated anyways.
Silver plated bananas will increase the resolution and attack of the sound. This is good if your system is very warm/slow sounding, but you can easily cross that "fine line" into the "too fast" area (depending on the resolution of your current system). If this happens, the music becomes too bright/harsh and can actually sound a bit sterile/artificial. It is just a matter of experimentation with your current system.
Silver plated bananas will increase the resolution and attack of the sound. This is good if your system is very warm/slow sounding, but you can easily cross that "fine line" into the "too fast" area (depending on the resolution of your current system). If this happens, the music becomes too bright/harsh and can actually sound a bit sterile/artificial. It is just a matter of experimentation with your current system.