Do pure copper banana plugs make a difference in the quality of the speaker sound.

I will say that what does NOT work is hard metals, like rhodium, or solid brass.

You want your plugs to be soft and non-tarnishing, preferably with a spring to them, like banana plugs have or the spring loaded WBT spades.

Anything hard like rhodium or gold over pot metal (like the Monster screw on spades) is never going to have a tight fit, especially when used in nickel plated speaker terminals.

Like the man said, don't be neurotic.  Use whatever connector comes on the end of the cable.  

Oh, and if you think you're gonna save some money putting your own on the end of some wire and do just as good, you're not. So that's another one you can not worry about.

i go bare wire when i can... i also go commando ;)

seriously, any decent made banana will do... just make sure contact is good

@ johnspain
As the poster above said "go commando", I agree!
For good sound quality go bare wire, tinned at both speaker and amp ends. Make sure both ends are very tight which is more important to sound quality then any connector will be.

Bare wire here too