On the speaker cones, I know plastic will last a lot longer. But what about sound quality? Is there a difference between paper and plastic?

 

I think most of the woofers available are poly coned for strength and reliability! The stronger cones flex less and create less distortion. A properly designed paper cone would act similar, and a poorly designed poly cone could sound worse.
Now the flex of paper or poly cones will also "color" the sound slightly, that can actually play into a good effect, not all speakers will sound identicle.....meaning you get to pick ones that sound best to you.