To terminate.. or not

You can shield the entire cable to reduce radiated EMI except for the termination. So how do you reduce radiated EMI at this point? The answer may be geometry of the termination. You probably want something flat and wide because it dissipates the magnetic field versus something long and narrow that concentrates the magnetic field. This is one possible reason for a spade over a banana.

Yes, should the washer(s) produce an ideal condition whereby pressure is applied relatively uniformly across the contact surface area - voila! :-)

Vbr,
Sam

Axle - Shielding is a very difficult thing. I assume you're talking about shielding speaker cables from external EMI radiation. I'm not sure that you need to shield speaker cables but in general shielding works a little different than we think. Shielding material of interconnect is non-magnetic but it is shielding cable not only from capacitively coupled but also electromagnetically coupled interference (common mode). EMI in fact IS electromagnetically coupled into the cable but because of skin effect it travels (to ground) on the outside of the cable's shield. Field inside of the shield is zero as long as cable is symmetrical/uniform.
When a cable shield is carrying differential mode current, as in the case of coax, skin effect will cause that differential mode current to flow on the inside of the shield.

Actually, I was talking about EMI radiating out of the binding post and onto adjacent compnoents/cables. Speaker cable doesn't need to be sheilded because it has low impedance and high current.

Axle - low impedance is only at low frequencies. At RF it appears as high impedance and also as amp's input since feedback is connected there (class AB amp has gain before feedback as high as 4000).

I would suspect that the highest radiation comes from power cables of amps that take high average power (class A). Current in power cables comes in narrow spikes of very high amplitude (it is really a switching power supply operating at 120Hz).