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

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 

Tinned with Cardas solder.